Objective To explore the changes of plasma fibrinogen and Ddimer during early insertion of peripherally inserted central catheter (PICC) in newly diagnosed lung cancer patients, and to provide reference for preventing PICCassociated thrombosis. Methods The values of plasma fibrinogen and Ddimer were measured at 1 day before insertion of PICC, and at the 3rd and 14th day after PICC insertion in 92 lung cancer patients who received firstcycle chemotherapy, and Doppler ultrasound was also performed to detect venous thrombosis at the same time. Symptoms of the extremity were observed every day during the study period. Results Ten patients developed PICCassociated thrombosis, accounting for 10.87% at the 14th day after PICC insertion. The values of plasma fibrinogen and Ddimer in those without PICCassociated venous thrombosis were increased at the 3rd day and decreased at the 14th day (P < 0.05 for all), whereas those in patients with PICCassociated thrombosis were linearly increased (P<0.05 for all). Conclusion The values of plasma fibrinogen and Ddimer in patients with lung cancer receiving firstcycle chemotherapy are significantly increased on the 3rd day after PICC catheterization, and we need to be highly vigilant to perceive PICCassociated venous thrombosis if they continue to increase after the 3rd day.