Abstract: The concentration of arsenic in subcellular fractions of rat liver is determined by differential centrifugation combined with epithermal neutron activation analysis (ENAA).The analytical quality has been verified by analysis of some standard reference materials. The results show that the distribution of As in subcellular fractions of rat liver cells is not homegeneous. The highest concentration of As is found in micrososme ,while the lowest content is found in nuclei for arsenic poisoned rat .The lowest content of As is noted in mitochondria of cotrast rats .The differences of As contents in subcellular fractions of lives cells between arsenic poisoned and normal rats are compared by means of t test and exceedingly significant differeces are found ( P <0.001). In As poisoned rat, the As content in microsome is significantly higher than that in other subcellular fractions ( P <0.05),except lysosome .