Objective: To evaluate the effect of breathing coordination in reducing catheter tip malposition during PICC inserting. Methods: Totally 250 cancer patients receiving PICC were randomly assigned to two groups. The control group (n=123) received routine care during PICC inserting, while the experimental group (n=127) received breathing coordination guidance instead of turning head coordination. The incidence and sites of PICC malposition were compared between the two groups. Results: The total incidence of PICC malposition in the experimental group was significantly lower than that of the control group (1.57% vs 11.38%, x²=10.033, P=0.002). Significant differences were found in the incidences of malposition in internal jugular vein and axillary vein between the two groups (p<0.05), while no significant differences were found in the incidences of malposition in internal thoracic vein, azygos vein and folding back in subclavian vein between the two groups (p>0.05). Conclusion: Patients’ appropriate breathing coordination can reduce the incidence of catheter tip malposition during PICC inserting, especially in reducing the incidence of malposition in internal jugular vein and axillary vein.