Nepal is one of the poorest countries in the world. Using the panel data of the Nepal Living Standard Measurement Survey (NLSS), the poverty rate in 1995–96 was estimated to be about 40%, while in 2003–04 it was estimated at roughly 30%. Political instability has prevented the development of industry and threatened the food security of poor people, but scholarship on the factors contributing to food security is incomplete; while the determinants of food security have been mentioned in past research, prior studies have analyzed cross‐sectional data and thus could not have omitted heterogeneity bias. This paper analyzes the change in agricultural productivity in real terms and the impact on household food security by using the panel data of NLSS in 1995–96 and 2003–04. This analysis reveals that growth is observed in real agricultural productivity in spite of land segmentation; the growth in agricultural productivity in real terms has a positive impact on household food security; and the lower a farmer's income becomes, the more positive its impact on food security. Therefore, advancements in agricultural productivity play a critical role in promoting food security at the individual and household levels.