Objective To evaluate the influence of the storing time of venous blood samples on the differential count of WBC by Sysmex XE-2100 hematology analyzer. Methods At room temperature, the precision of the differential count of WBC by Sysmex XE-2100 hematology analyzer were tested. 38 samples were taken the differential count of WBC by Sysmex XE-2100 hematology analyzer after stored for 0, 2, 4, 8, 24 and 48 h. Differential count of WBC was also taken under microscope for comparison. Results The precision of differential count of WBC by Sysmex XE-2100for all the samples was in the allowable range. The correlation coefficient of the differential count of WBC by two methods for neutrophils, lymphocytes, monocytes, eosinophils and basophils were 0.9859, 0.9775, 0.8053, 0.8695and 0.5243 (P<0.01). There was insignificant difference in the test at 8h, very significant difference of MONO and EOS at 48 h. Differences of EOS, MONO between two methods were significant increased at 8 h. Conclusion At room temperature, the differential count of WBC of venous blood samples by Sysmex XE-2100 hematology analyzer should finish within 8 h.