The study sought to investigate the effect of cost of production on financial performance of selected poultry rearing farmers in Kiambu County, Kenya. The study was guided by specific objectives in cluding; the effect of feed costs, the effect of poultry equipment, the effect of brooding costs and the effect of medication costs on financial performance of selected poultry rearing farmers in Kiambu County, Kenya. The study was anchored on cash conversion cycle theory, transaction cost of economics theory, resource based theory and operating cycle theory. The study adopted descriptive research design and a sample size of 350 respondents. Snow ball sampling method was used to reach the respondents since their location was not well defined. Primary data was collected using questionnaires that was pilot tested to ensure its valid and reliable. Descriptive statistics of mean, percentages and standard deviation and inferential statistics including multiple regression analysis were conducted. The study findings revealed that production cost including feeding cost, poultry equipment, brooding cost and medication cost all individually had a statistically significant effect on financial performance and therefore all the null hypotheses were rejected. Feeding cost and medication cost had negative statistically significant effect, hence concluding that when the cost for feeds and medication increases, they lead to a decrease in financial performance. Also increase in poultry equipment and brooding cost were found to positively affect performance concluding that when the farmers increase investment in relevant equipment and brooding, financial performance improves. On feeding cost and medication cost, the study recommends that the farmers through the regulators to lobby for subsidies from the government so as to lower the cost of production. The study further recommends the farmers to invest in heavy technology in terms of equipment and brooding costs since greatly increase their financial performance.