Radiotherapy causes various complications including low immunity. Past research has shown that the low immunity is due to the low amount of lymphocytes and consumption of citrullus vulgaris will alleviate this problem. Based on this a study was conducted to identify how citrullus vulgaris was able to produce radioprotection on the lymphocyte membrane. A total of 30 adult male Sprague-Dawley rats were used and divided into three equals groups of positive control, negative control and treatment. For seven days, positive control and negative control were force fed with normal saline of 40 ml/kg animal weight while the treatment group received 40 g/kg animal weight fresh juice of citrullus vulgaris daily. After a week positive control and treatment group were irradiated with 0.9 Gy gamma ray. Viable lymphocyte were determined using propidium iodine and acridine orange stain. Results clearly shows that positive control, negative and treatment group were significantly different at 34 3% , 80 2% and 71 2% respectively. SEM results shows that pores were present on the membrane of the positive control while the negative control had none. Similar results were also found on the treatment group. Based on the result it had shown that citrullus vulgaris had radioprotection properties and lymphocytes were destroyed by the formation of pores on their membrane. It is very likely that the radioprotection properties could be due to the presence of antioxidants particularly vitamin A, C and lycopene. In conclusion, citrullus vulgaris could be used as a safe radioprotection agent.