In the current era of information change, human resources accounting is an increasingly important part of an organisation’s total wealth. It should form parts of the assets in the financial statements under the non-current assets. Thus, this study examines the effect of human resources accounting cost information proxied by training and development cost and personnel cost together with firm size (introduced as a control variable) on investment decision proxies using ROI of listed assurance companies in Nigeria. The ex-post facto research design was adopted with a population of 23 companies, of which 15 were sampled using purposive sampling techniques. Secondary data sources from annual reports of listed assurance companies in Nigeria ranging from 2013 to 2022 financial years were used. Panel regression analysis was used to analyse the result using E-views 10. The result of the study revealed that training and development costs had a positive and significant effect on the Return on investment of listed assurance companies in Nigeria. At the same time, personnel costs also had a positive and significant effect on the Return on investment of listed assurance companies in Nigeria. Based on this finding, it is recommended that assurance companies invest more in their employees’ training and development and increase their staff welfare to enhance human capital efficiency.