In this article, we study the substitution between leasing and bank loans in financing the investment of small companies. The analysis is based on financial information about Polish companies listed on NewConnect, which used financial leasing in the period of 2012–2016. We argue that leasing and bank loans are the substitute in financing the investment of small companies. We estimate the probability of financial leasing and its size using the tobit and logit models. We find that financial leasing and bank loan, for Polish small companies, are complementarity. Our empirical results indicate that financial leasing and bank loans are complementary sources of financing investment in fixed assets. Also the higher the usage of financial leasing, the higher the likelihood that the enterprise is indebted because of long-term bank loan – complementarity.