In this article the dynamic retention of fission products ,134,Cs and ,147,Pm as well as the proliferation ability on cells of bone marrow and thymus of rats were investigated. The retention equation of ,134,Cs was well described by a two-exponential function, that is: R(t)=18.04 e-,9.3175t,+45.13 e-,0.0423t,. There are two retention components, fast and slow. The effective biological T,1/2, were 0.07 and 16.14 days respectively. While the retention equation of ,147,Pm is: R(t)= 0.199e,-0.1452t, +0.812 e,-0.0008t,. Where the fast component T,1, was 4.77 d; and the slow compoment T,2, was 866.3 d. Results show that the proliferation of bone marrow cells and thymus cells were excited with a low dose internal irradiation of ,134,Cs from 0.37 to 1.85 kBq/g and of ,147,Pm from 0.185 to 0.74 kBq/g. It showed that a stimulatory resporse of cell proliferation induced by low doses of ,134,Cs and ,147,Pm has been obser ved.