Converting food waste into animal-feed is highly useful for tackling the problem of food waste, which is particularly severe in developed countries. This study quantified inefficiencies in converting food waste into animal-feed and identified their causes through a data envelopment analysis (DEA) of the monthly input–output data of two producers of animal-feed obtained from food waste in Japan. Our empirical analysis revealed that the producers of animal-feed obtained from food waste (especially those treating food waste from retail and service industries) demonstrated inefficiencies in production technology and scale; moreover, expanding the production scale and improving the quality of food waste could enhance production efficiency. Based on the empirical results, specific policy implications were provided for the widespread use of animal-feed obtained from food waste in Japan and elsewhere, globally. Furthermore, it was found that the COVID-19 pandemic contributed to a severe reduction in the production efficiency of animal-feed producers treating food waste obtained from retail and service industries.