Five isonitrogenous (23% CP) and isocaloric (2.8 Mcal/kg) diets were prepared and used in this study; two control diets (diet 1, no date pits; diet 2, no date pits + 300 mg/kg vitamin E) and three diets containing date pits (diet 3, 12.5% date pits (DP); diet 4, 12.5% DP + 300 mg/kg vitamin E; and diet 5, 25% DP). Ninety mature Wistar rats (45 females and 45 males) were used in this experiment. All animals were provided with feed and water on an ad libitum basis for 29 consecutive days. Water and feed intake were measured daily Body weights were measured weekly, at the beginning, and the end of each experimental period. Rats were killed by stunning in day 30 and blood samples were collected. Blood serum was analysed for testosterone, oestradiol levels, and for some blood biochemical parameters. Adipose tissue and certain vital organs were excised and weighed. Chemical analyses were done for date pits, experimental diets, and rats’ carcass to determine crude protein, crude fiber, crude fat, and ash. Results of the approximate chemical analysis of date pits indicated that the nitrogen free extract (NFE) was 71.5 % and only 3 % was starch. When chemical analysis was based on dietary fiber, the NFE was calculated and found to be 26.7% of which 78 % is mannose. Because of the low carbohydrate content in date pits, the total replacement of high energy grain by date pits is not recommended. Feeding date pits up to 25% to rats enhance the growth of the experimental animals. This may be due to factor(s) other than carbohydrate content in date pits. No effect was observed on water intake. The dietary treatments had no significant effect on feed intake for both male and female rats. The only exception was when vitamin E was added to the control diet in week 1 and 2 in male rats. Also, there were no significant effects on body weight gain for both experimental animals. The only exception was a significant increase in weight gain for male rats in diet 2 during week 1, and for female rats in diet 5 during week 4. The dietary treatments had no significant effect in spleen and adipose tissue weight. Concerning, blood biochemical parameters globulin concentration was within the normal range. Total protein concentration was within the normal range for male rats in diet 4 only, and in diet 3 and 5 for female rats. Diet 1, 2, and 3 for male rats were within the normal range for GPT concentration. The dietary treatments had no effect on testosterone level in male rats. While, oestradiol concentration in the serum of female rats decreased significantly as the percent of date pits increased. The addition of date pits and vitamin E to the diet had the same effect in reducing the oestradiol level in the serum of the female rats, this may be due to estrogenic effect of date pits, which may cause reduction in the fertility of the female rats