This article analyzes the determinants of labor productivity in micro, small and medium-sized enterprises in Mexico (MSMEs), with the aim of bringing key variables to the attention of economic policy to compensate for the negative effects of the COVID-19 pandemic. Panel data estimates are used for the federal entities of the Mexican economy. The main empirical finding is that the most important determinant of the product per worker of MSMEs is the gross formation of fixed capital per worker and its effect increases along with the size of the company. The distribution of profits, benefits and salaries per worker has a less important effect and loses relevance as the size of the companies increases.