Hematogenous metastasis always leads to the poor prognosis of non-small cell lung cancers (NSCLC). Activated platelets are involved in hematogenous metastasis and may be a potential therapeutic target. P-selectin is an important adhesion molecule and expressed on the surface of activated platelets. P-selectin glycoprotein ligand-1 (PSGL-1) as a transmembrane protein is expressed on the surface of various cell types. P-selectin can bind to PSGL-1, and thereby initiate the platelet-mediated cell adhesion. The aim of the study was to investigate the degree of platelet activation in NSCLC and the roles of PSGL-1 in the activation of platelets. Purified platelets were obtained from NSCLC patients (40 lung adenocarcinomas and 26 lung squamous cell carcinomas), and P-selectin expression was detected by fluorescence-activated cell sorter. The population of peripheral blood platelets with P-selectin expression in lung adenocarcinoma was 63.16 ± 25.44 %, and significantly higher than that in lung squamous cell carcinoma (35.97 ± 17.19 %) and the healthy population (9.12 ± 7.66 %, n = 30). A specific small hairpin RNA (shRNA) for PSGL-1 was transfected into A549 human alveolar cell carcinoma cells. The expressions of PSGL-1 mRNA and protein were significantly reduced with the PSGL-1 shRNA (p < 0.01). Furthermore, the knockdown of PSGL-1 also resulted in the significantly reduced aggregate formation of activated platelets and A549 cells. Thus, activated platelets may interact with lung cancer cells through PSGL-1. Inhibiting platelet activation and/or down-regulating PSGL-1 expression may be useful for suppression of tumor metastasis.