Objective To investigate the combined biological effects of low dose radiation,carbon monoxide,benzene and noise on rats.Methods Sixteen male SD rats were randomly divided into experiment group and control group.The experiment group was exposed to carbon monoxide,benzene,low dose radiation and noise daily,the control group was in common environment.Peripheral blood,organ index,and marrow DNA content were detected.Two-dimensional electrophoresis (2-DE) was performed on serum protein analysis.Differential expressed proteins were identified by a matrix assisted laser desorption/ionization time of flight mass spectrometry (MAIDI-TOF-MS).Results Compared to control group,the liver index,spleen index,thymus index,leukocytes,platelets count,and marrow DNA content of the experiment group were decreased significantly (t =2.732,4.141,3.053,2.211,2.668,11.592,P ＜0.05).12 altered proteins were detected and through identification,3 proteins were definite in terms of serum amyloid A-4 protein (SAA4),trichoplein keratin filament-binding protein (TCHP) and tubulin alpha-4A chain (TUBA4A).Conclusions The hematopoietic system and immune system of rats are damaged significantly with the changes of several serum protein expressions by the combined exposure of low dose radiation,carbon monoxide,benzene and noise.This study may provide new information for the mechanism of the combination effects.