Abstract: Objective to assess the influence of administering the tryptophan in the white male rats Rattus novergicus's testosterone and estradiol hormone levels. This research is experimental with the design of the posttest only control group design. The samples used as many as 28 rats were divided into 4 treatment groups. Each group is given an intraperitoneal injection of tryptophan with a dose level of 40mg, 50mg and 60mg/kg of bady weight. While one group was separated and made as control group. The treatments are given for 14 days and measured hormone levels using RIA. Based on assessment results, it was observed that there was a decrease in the average levels of testosterone (13,78nmol/L) and also observed an increase in the average level of the estradiol (8,65pg/dl) in the male white rat Rattus norvegicus when compared to the control group. The doses of tryptophan administered in the treatment group 1 is 40mg obtained the average testosterone levels 12,95nmol/L and average estradiol level of 9,87pg/dl. The doses of tryptophan administered in the treatment group 2 is 50mg obtained an average testosterone level of 11.03nmol/L and average estradiol level of 10,17pg/dl. The administration of tryptophan caused a decrease in the average testosterone levels in the control group and an increase in the average levels of estradiol compared to the control group even though the increase and decrease in the mean was not significant. It is likely that intraperitoneal administration of tryptophan has inhibitory effect of estradiol on testosterone.