In the following study, dietary fiber, insoluble (IDF), soluble (SDF) and total (TDF) were determined in cereals and by-products and in commercial cereals products which are found in the national market and promoted as a source of fiber. The Prosky's enzimatic-gravimetric method was used. Results were expressed as g/100 g wet basis. Total dietary fiber in cereals and by-products showed a range from 1.18% (poshed rice) to 89.10% (com bran). For the commercial cereal products, the TDF values varied from 3.73% (rice-sesame cookies) to 34.96% (Breakfast cereal named All Bran). The FDI values always were greater than the SDF values. Based on this fact, FDI values were compared with NDF (Neutral Detergent Fiber) values reported in the scientific literature and in the Venezuelan Food Composition Tables using a regression analysis. FDI values were always greater than NDF values and the correlation factor (r) was high and statistical significance to P<0.05 for both food groups in study.