OBJECTIVE To assess the influential factors of STR genotyping in 10% unbuffered formalin fixed paraffin embedded samples. METHODS Eight kinds of autopsy samples including heart, brain, liver, spleen, kidney, lung, stomach and intestine tissue from 2 corpse were fixed with 10% unbuffered formalin and embedded with paraffin according to the routine procedure from which the DNA were extracted with three different methods (QIAGEN, IQ and Chelex). STR profile were analyzed with AmpFlSTR Identifiler Kit and capillary electrophoresis on genetic analyzer 3100-Avant. STR profiles of 56 archival paraffin embedded samples from 15 cases were also analyzed with methods as mentioned. These archival samples, including heart, liver, lung and intestine tissue, had been preserved for 1 to 5 years in ambient temperature. Effectiveness of STR genotyping was assessed with the recalling ration of the 15 STR loci composing of the Identifiler Kit. RESULTS Significant difference of the recalling ration was statistically revealed among the different types of paraffin embedded sample with same preserving period. Moreover, the STR recalling ration was continuously lowering with the prolongation of preserving period in all of the samples. The linear relationship between the STR recalling ratio and the preserving period was showed in lung and heart sample. The STR recalling ration in lung sample was higher than that in the other types of paraffin embedded sample. CONCLUSIONS Preserving period, tissue type, extracting method of DNA and the PCR template concentration were the most important influential factors for successfully STR genotyping paraffin embedded samples, which fixed with unbuffered formalin for the same time.