Abstract: Rhizobium was used in the study with the term of "bacterium capacity" of soil to describe the quantitative changes of viable rhizobia in soil and to discuss its ecological and agtronomic significances. The term meant the highest population per unit soil and was. expressed in cell numbers/g dry soil generally. The rule of quantitative changes of viable Rhizobium in sandy soil and heavy loam. Inoculum density of Rhizobium influence the effect an application were also discussed.The results showed that there was a definite rhzobium capacity in both surveyed heavy loam and sandy soil under certain conditions. The effect of rhizobial cell number at the beginning of experiment on the rhizobium capacity was signigicant in natural soil. It was found that the higher the starting cell number, the higher the rhizobium capacity, whetherthere was legume growth or not. In treatments with different initial number of 104 or 2 x106, the number of rhizobia differed only times of tens each.When soil sample was first sterilized then rhizobia was added in, initial cell number had little effect on rhizobium capacity. In the four treatments in which the starting cell number differing in 105 or 106 times, the rhizobium capacities were similar. That meant that in the soil with low starting cell number rhizobia grew abundantly. The rhizobium capacities of heavy loam and sandy sosul were close.