Yield potential of rice (Oryza sativa) is often reduced by one or more factors that damage or reduce leaf area of the plant. Even though the importance of defoliators is recognized, little is known about the relationship between leaf area removed and yield loss. The objective of this study was to determine the response of upland and irrigated rice in relation to defoliation imposed in different stages of plant development. The experiment was carried out at Embrapa Rice and Beans Experiment Station, located near Goiânia, GO, Brazil, in upland and low land conditions. The experimental design was split plot arranged in randomized complete blocks, with four replications. The main plots were rice growth stages (beginning of tillering, maximum tillering, flower differentiantion, and heading) and subplots were defoliation levels (0, 25, 50, 75 e 100 %). Measurements of flowering and harvest time, number or tillers and panicles, yield and grain quality were taken from the two 3.0 m center rows. The results indicated that removing leaf area impacts yield in all plant growth stages in both upland and flood cultivation environments. However, yield was more affected when defoliation was imposed during reproductive rice stages. The percentage of broken kernels in milling was higher only when defoliation occurred at heading stage. Flowering time and seed weight were not affected by defoliation.