The aim of this study is to investigate the impact of investment inefficiency on the sustainability performance of companies, considering the moderating role of economic policy uncertainty. Investment inefficiency, as one of the key factors in the inefficient allocation of financial resources, can affect the ability of companies to achieve economic, social, and environmental goals. This study used the multivariate regression analysis method and panel data from companies listed on the Tehran Stock Exchange during the period 2015-2016 with a sample of 120 companies. To measure sustainability performance, 60 indicators were extracted in three dimensions: economic, social, and environmental, and were measured using a dummy variable between zero and one. The findings showed that investment inefficiency has a negative and significant impact on sustainability performance, such that increasing inefficiency in capital allocation reduces the ability of companies to implement social and environmental responsibility projects. Also, the study of the moderating effect of economic policy uncertainty showed that in conditions of high uncertainty, the negative effect of investment inefficiency on sustainability performance is intensified. This result indicates the importance of efficient capital management and special attention to sustainability projects even in conditions of economic uncertainty. The present study recommends that managers and policymakers improve the sustainability performance of companies by improving the investment process, increasing transparency, and allocating resources optimally, while reducing inefficiency. The findings of this study can also be used as a basis for decision-making in economic policies and long-term planning of companies.