Unlike the traditional finance model, Islamic finance is based on its own principles, outlined by the sharia provisions regarding the management of money in Islamic law. The most important of these principles are profit and loss sharing, risk sharing, interest prohibition, the principle of basing transactions on goods, and the prohibition of investing in extreme uncertainty. In addition to these principles, Islamic law prohibits investing in interest-based financial institutions and some sectors that Islam does not approve of such as alcohol, adult films, pork, etc., and refrains from cooperating with these sectors. The Islamic financial system has been established to take into account social and moral issues as well as acting on religious principles. Islamic finance has implemented Islamic indices as a guide for those who want to invest in Sharia-compliant stocks. The main purpose of Islamic indices is to inform which company stocks are suitable in terms of sharia. Qualitative and quantitative criteria must be met in order to be included in Islamic indices. Qualitative criteria are related to the fields of activity of companies. However, quantitative criteria consist of financial constraints. One of the financial constraints is the rate of investment in working capital components in total assets. The most important reason for this is that some of the working capital components generate interest income. Working capital is the portion of companies' assets that are expected to be converted into cash within one year. Therefore, the ratio of these assets in total assets is important for companies' risk, profitability, and liquidity. In conclusion, the main research question of this study is how financial restrictions in Islamic indices affect the working capital management of companies. There are quite a few studies on Islamic indices in the literature. Most of the studies are related to the structural characteristics of these indices. Likewise, there are many publications on the financial performance of these indices. However, studies on working capital management of companies included in Islamic indices are quite limited. In these studies, the relationship between working capital and profitability has been examined. As a result of the literature review, no academic study was found on the working capital management efficiency of companies in Islamic indices. Therefore, this study is the first study done on this subject. In particular, the effect of restrictions on current assets (working capital components) on working capital management has been investigated for the first time. Calculation of working capital management efficiency in the study was determined by the index method developed by Bhattacharya (1997). This method consists of calculating three indices. These are performance, utilization, and efficiency indices. Working capital components (cash and equivalents, trade receivables, other trade receivables, inventories, prepaid expenses, and other current assets) and sales of the company are taken into account in the calculation of the three indices. In this study, Participation 30 index companies serving as an Islamic index were selected as the universe of the research. However, not all of the 30 companies that make up this index are included in the analysis. In addition, not all types of companies need working capital management. Working capital management is essential for manufacturing industry companies. Therefore, only manufacturing industry companies were selected in this study. Since there are 17 manufacturing companies in the Participation 30 index, these companies constitute the universe of the study. Financial sector companies supplying the financing of manufacturing industry activities were excluded from the scope of the study. In addition, companies in the retail sector that do not produce commodities are not included in the analysis. In the study, the six-year balance sheet and income statement data of the companies between 2013 and 2018 were used, and these data were obtained from the public disclosure platform. According to the results obtained from the study, the performance index of 65.69% of the companies, the usage index of 55.89%, and the efficiency index of 67.65% were higher than 1. In other words, these companies have been successful in managing working capital. To sum up, it is concluded that the restrictions imposed by Islamic indices on working capital components do not adversely affect the effectiveness of companies' working capital management.