Objective To unravel the relationship between Toll-like receptor 4 (TLR4) expression in platelets and the activation of platelet in thrombocytopenia (TCP) in case of sepsis. Method A total of 64 patients with sepsis were prospectively studied with control. Platelet count (PC), mean platelet volume (MPV),platelet distribution width (PDW),platelet TLR4 expression, platelet PAC-1 expression, sCD40L and TNF-α concentrations were compared between healthy control group (15 cases) and sepsis group on admission and 3 d,Sd,and 9 days after admission. The changes of MPV and PDW in TCP and non-TCP subgroups of sepsis before and after treatment were recorded. Prognostic index was analyzed. Results The PC was lower in sepsis group (P=0.006), and MPV and PDW were higher in sepsis group than those in healthy control group (P = 0.046, P =0.001). Platelet TLR4 and PAC-1 expressions, and sCD40L and TNF-α levels also increased more significantly in sepsis group (P ＜ 0.001). PAC-1 expression and TNF- level were higher in TCP group than those in non-TCP group before and after treatment (P = 0.023, P = 0.011). The sCD40L concentration and platelet TLR4 expression were significantly higher in treated TCP groups than in non-TCP group (P = 0.047, P = 0.001). Compared with non-TCP,the rate of bleeding was higher (P = 0.024) and the length of ICU stay was longer (P = 0.013).The APACHE Ⅱ score and the 28-day mortality were higher in TCP group (P ＜ 0.01, P = 0.048). Conclusions The elevation of platelet TLR4 expression in sepsis along with platelet activation is closely related to the incidence of thrombocytopenia. The occurrence of TCP is a poor prognosis sign of sepsis.