Thirty rats were divided into three groups: Damp group (relative humidity was over 90% and temperature 18--25*C ), Cold group (T: 2 -+ 2"(2, RH: 54 -+ 4 % ) and normal control group ( T: 18--25"(2, RH: 54-+ 4%). The resu!t.s showed that number of Escherichia coli increased greatly while number of bifidobacterium reduced in high moisture. In Damp group, level of secretory IgA was much higher as compared with that of the normal controlled and Cold group. Th/i and Ts/c in Cold group and in Damp group were slightly lower than that in the normal group. Light microscopic examinations showed that there were infiltration of inflammatory cells and low-grade hyperemra in the phalangeal joints' synovium of rats of the Damp group in pathological section. Meanwhile there were low-grade erosion, degeneration, necrosis and exfoliation in epithelium mucosa of small intestine. KEY WORDS dampness, enteric bacilli, secretory immunoglobulin A, pathology, rat