Drought stress is one of the most important environmental factors that limit lentil production. In order to evaluate the effect of drought stress at flowering and pod filling stages on growth indices of lentil cultivar Kimiya, an experiment was carried out at the research greenhouse of Higher Educational Complex of Saravan, using a completely randomized design with four replications. Drought stress was applied by lack of irrigation until the soil moisture reached to 20 percent of field capacity at stages of flowering and pod filling stages. In this experiment, growth indices including Plant leaf area (PLA), relative growth rate (RGR), Plant growth rate (PGR), net assimilation rate (NAR) were measured. Results showed that the flowering stage in lentil plant is more sensitive to drought because at flowering stage decreased LAI, RGR, PGR and NAR. Overall, the results indicated that at the end of growing season, PGR declined due to the stopping of vegetative growth, senescence of leaves, the reduction of NAR and the allocation of assimilates to the seeds.