Objective To study the effect of anti-hypertensive therapy on the characteristics of platelet in essential hypertension(EH) patients. Methods Thirty-two healthy people(CT) and 37 patients with primary hypertension (gradeⅠ) were recruited . Blood pressure and 4 platelet parameters: platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW) and platelet hematocrit (PCT) were determined by whole blood automatic analysis apparatus. Results The 4 platelet parameters were increased in hypertension patients compared with healthy people and decreased after anti-hypertensive therapy[PLT:(before 201.8?72.9 vs after 187.1?68.6 )10~ 9 L+{-1}; MPV:(before 10.3?1.9 vs after 10.0?1.9)fL, PDW:(before 15.5?1.1 vs after 15.2?1.0)fL; PCT:(before 0.198%?0.047% vs after 0.187%?0.036%)](P