Abstract: An experiment was conducted to determine the effect of different protein resources on concentration of small peptides (SP) (Pro-Ala, Val-Val, Pro-Leu, Met-Met) in the rumen fluid. Four sheep fitted with permanent cannulas were used in a 4×4 Latin square design, and fed four different protein resource which contain soybean, casein, fish meal and corn gluten meal respectively. The CP levels of four experimental diets were 14% and the ratio of concentrate and forage was 3∶7. The dry matter intake was 1 kg/d per sheep with equal to 1.2 times maintain for metabolizability energy. The results showed that the concentration of SP in rumen fluid varied with the time of protein resource degradation, the concentrations of most sheep reached a peak after 2 h to 6h. For fish meal, corn gluten meal and soybean meal treatments, accumulated amount of SP during the time of 6 hours was: Pro-Leu＞Val-Val＞Pro-Ala＞Met-Met, the accumulated amount of SP during the time of 6 hours for casein was: Pro-Leu＞Pro-Ala＞Val-Val＞Met-Met. Experiment results proved that first amino residue from N-terminate of the SP was proline, and the SP which had hydrophobic structure, or either of structure with proline residue from N terminate can resist to rumen degradation.