Purpose: This study aimed to investigate the impact of CYP3A4*1G genetic polymorphism on metabolism of fentanyl in Chinese patients undergoing lower abdominal surgery. Methods: 176 patients receiving elective lower abdominal surgery under general anesthesia were recruited into this study. Genotyping of CYP3A4*1G was carried out by direct sequencing. The plasma fentanyl concentration was detected 30 min after anesthesia induction by high performance liquid chromatography-ultraviolet ray (HPLC-UV). The visual analog scale (VAS) was used for pain evaluation at rest during patient-controlled analgesia (PCA) treatment 0 h, 12 h and 24 h after operation. PCA fentanyl consumption and adverse effects were recorded during the first 24 h after surgery.