Intracavitary electrocardiogram (IC-ECG) guidance is widely used for peripherally inserted central catheter (PICC) placement. The P wave variation has rarely been reported in persistent left superior vena cava (PLSVC). Here, we report a PLSVC case of P wave variation in PICC placement guided by IC-ECG. In this case, the P wave variation of the PLSVC was quite different from that of the right superior vena cava (RSVC). The tip of the catheter was located at the lower segment of the left superior vena cava according to postoperative radiography examination. PICC functioned normally, and no complications occurred.