Chemical determinations of the carbohydrates fractions that constitute the total carbohydrates (TC) and ruminal kinetic studies of the neutral detergent fiber (NDF) of some feeds obtained under tropical conditions, were made. The grasses tifton-85, elephant, palisade, signal, molasses, the perennial soy, the corn silage, the hays of coast-cross, signal, and the concentrates soybean meal, cottonseed meal, wheat bran, corn meal and ground sorghum grain, were studied. The slow but ruminally digestible carbohydrates (fraction B₂), the indigestible fraction C and the fast and intermediate ruminally digestible carbohydrates (fraction A+B₁) were analyzed. The fractions, as percentage of TC, varied from .74 to 87.98% for fraction A+B₁, from 8.10 to 76.79% for fraction B₂, and 3.90 to 36.79% for fraction C. The NDF degradation rates varied from 1.93 to 6.24%/h and the effective degradability from 16.73 to 35.48%. The variations of the carbohydrate fractions, NDF degradation rates, and the dynamics of the polymeric constituents of the cell walls, along its residence time in the ruminai ambient, should be considered for the energy adequacy in the rumen and intestine.