The present study was conducted to estimate  the dietary fiber fractions in raw and steamed broccoli and cauliflower, as well as to evaluate the biological values of them using experimental animals. Generally it was found that raw and steamed broccoli and cauliflower had a significantly high amounts of dietary fiber fractions. Raw broccoli contained higher amounts of neutral detergent fibers (NDF) and acid detergent fibers (ADF)  (37.64 and 31.99%) than raw cauliflower (32.70  and 26.71%) respectively. On the other hand no significant difference was noted in acid detergent lignin (ADL) and hemicellulose between raw broccoli and raw cauliflower. The cellulose content was higher in raw and steamed broccoli (15.96, 10.59%) compared with raw and steamed cauliflower (9.82, 8.48%). Pectin content was 27.30% and 30.38% for raw broccoli and cauliflower respectively. Barely significant reduction in all the dietary fiber fractions was noticed in both broccoli and cauliflower after steaming. Biological evaluation of raw and steamed broccoli and cauliflower was investigated using experimental animals (rats). Data revealed that the lowest weight gain was for the rats which fed on diets contained raw broccoli (50.00g) followed by that contained raw cauliflower (61.67g), while the highest weight gain was observed for the group fed on basal diet (80.00g). Meanwhile feeding the rats on steamed broccoli or cauliflower raised their weight gain by 65.00 g and 72.50 g, respectively. Moreover, the results showed that feeding the rats on diets contained broccoli or cauliflower (raw or steamed) for 40 days remarkably lowered their blood lipid fractions as total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C) and triglycerides (TG) compared with those fed on basal diet but the high density lipoprotein cholesterol (HDL-C) was increased . Also, the blood glucose in the animal's blood was reduced by 20.99% and 12.92% for rats fed on raw and steamed broccoli diets and by 20.22 % and 13.65% for those fed on raw and steamed cauliflower respectively, compared to the basal diet groups.