Abstract: Narrow genetic base is a main problem hindering the progress of physic nut breeding. The objective of this study was to compare the effects of different levels of gamma radiation on germination percentage, survival percentage and growth of five physic nut genotypes. The seeds were treated with six levels of gamma radiation (0, 200, 400, 600, 800 and 1000 Gy) and the 5x6 treatment combinations were arranged in a randomized complete block design with three replications. Data were recorded for germination percentage, survival percentage at 15 Days After Germination (DAG) (GR50(15)) and survival percentage at 30 DAG (LD50(30)). As the seedlings did not survive at 600, 800 and 1000 Gy, these treatments were deleted from the successive evaluations of plant height, stem diameter and leaf number. Higher doses of gamma radiation resulted in the significant reductions in germination percentage, survival percentage and plant height. The germination percentages were from 4.0% for 1000 Gy to 82.5% for 0 Gy. The seeds treated with gamma radiation higher than 600 Gy resulted in complete mortality. Difference among genotypes was not significant for these characters. The dosages of gamma radiation to obtain LD50 based on survival percentage 30 DAG was 425 Gy and was not dependent on genotypes. The information is useful for gamma radiation induction of mutation breeding for physic nut.