Aim To observe the effects of high low density lipoprotein cholesterol (LDLC) and fluvastatin on PAC-1 and CD40L expression of platelets in vitro and vivo and investigate its mechanism. Methods In vivo experiments,before and after treatment of fluvastatin for high LDLC patients,the CD40L and PAC-1 positive rate of platelets by flow cytometry were examined under the same conditions. The CD40L and PAC-1 expression of each group were compared. In vitro experiments,after the co-incubation of these chosed plasma or LDLC with the same healthy platelets and the interference with fluvastatin,the PAC-1 and CD40L positive rate of platelets were tested by flow cytometry and platelets total CD40L protein content by Western blotting and CD40L mRNA were examined under the same conditions in all objects. The PAC-1 and CD40L positive rate,the total CD40L content and CD40L mRNA of each group were compared respectively. Results Not only in vivo study but also in vitro study,the platelet PAC-1 and CD40L positive rate in high LDLC group were significant higher than in control group(P all<0.01). Followed the LDLC concentration decrease,the platelet PAC-1 and CD40L positive rate decreased after the treatment of fluvastatin in vivo,but in vitro study,the fluvastatin didn't affect the expression significantly. LDLC itself didn't affect the platelet PAC-1 and CD40L positive rate in