Hebei Province is one of the main distribution areas growing wild soybean( Glycine soja ) in China. In this study, 461 seed samples,collected from 18 natural populations in this province, were used to electrophoretically observe the change in forms and their frequencies of the Kunitz trypsin inhibitor protein (KTI)in individual populations and geographical areas. Allelic frequencies accounted for 85% for Tia and 15% for Tib in the total samples. Twelve populations examined were polymorphic at the KTI locus, accounting for over 50% in the populations investigated. Four populations, 22% of all the populations, were found to have natural cross-pollination with varied heterozygote rates of 3% -5.5%, and the average was 1% in the total sampies. Geographically, the mean Tib frequency in the north areas was higher than in the south, and higher in the mountainous area than in the plain areas. The populations in a lake ecological environment (Baiyangdian Lake) were almost monomorphic. No obvious relationship between the frequency and the geographical distance was observed. In addition, we first found a mutation for the absence of the KTI in wild soybean.