Abstract：Objective To investigate the reasons for pseudothrornbocytopenia. Methods Venous bloods of 5 patients with pseudothrornbocytopenia were collected with dipotassium EDTA and sodium citrate respectively．Their PLTs were measured by the hematology analyzer, and blood smears were made for microzscope observation. Results PLTs of the 5 samples were in normal reference when they were measured immediatly. After 30 minutes, for EDTA-K2 anticoagulanted bloods，PLTs were significantly decreased and aggregated in blood smears. For sodium citrate anticoagulanted bloods, PLTs were in normal range and scattered in blood smears. Conclusion EDTA-K2 could accelerate the PLT aggregation and cause pseudothrornbocytopenia in some patients.