Objective: To investigate effects of Agaricus blazei polysaccharide (ABP) on rat thymocyte apoptosis and mitochondrial membrane potential which were induced by dexamethasone (DEX). Method: Forty Wistar rats were divided into four groups randomly with 10 in each group. The four groups were as follows: normal group

model group

low dose ABP group and high dose ABP group.Normal group and model group were prepared by normal saline solution; low dose ABP group and high dose ABP group were prepared by ABP solution(60

120 mg·kg-1)

once a day for seven days continuously. Model group and low dose ABP group were injected through belly by DEX(0.02 g·kg-1). All groups were killed three hours later and rat thymocyte was taken out clenly. Mcroscopic observation and flow cytometry were used to observe morph ological changes and apoptosis of rat thymocyte

percentage of deoxyribonucleic acid(DNA) strand breakage

mitochondrial membrane potential changes and contents of superoxide dismutase (SOD) in rat thymocyte and malomialdehvde (MDA). Result: Mitochondria cristal dilatation of thyocyte obviously released in ABP group compared with model group. Rate of rat thymocyte apoptosis in ABP group [low dose(5.96±1.14)%

high dose(5.07±1.02)%]

DNA breakage rate[low dose(3.67±0.49)%

high dose(3.24±0.45)%]and MDA content in rat thymocyte [low dose(1.87±0.25)μg·mg-1

high dose(1.72±0.23)μg·mg-1] were obviously lower than model group[(7.14±1.62)%

(4.25±0.86)%

(2.16±0.38)μg·mg-1]; mitochondrial membrane potential in rat thymocyte (fluorescence index:low dose 38.57±6.29

high dose 41.36±7.18)and SOD conten in rat thymocyte [low dose(25.78±3.94)μg·mg-1

high dose(27.36±4.21)μg·mg-1]; mitochondrial membrane potential in rat thymocyte (fluorescence index:low dose 38.57±6.29

high dose 41.36±7.18)and SOD conten in rat thymocyte·mg-1

high dose(27.36±4.21)μg·mg-1]were significantly higher than model group(32.76±5.48) fluorescence index

(21.45±3.52)μg·mg-1. Conclusion: ABP prevent DNA strand breakage and the decreasing of mitochondrial membrane potential which can inhibit rat thymocyte apoptosis induced by DEX. The mechanism may be that ABP strengthen antioxidan function of thymus.