Abstract: Objective To evaluate the effects of auxiliary surface markers technique(ASM) in reducing setup errors in radiotherapy for patients with nasopharyngeal carcinoma(NPC). Methods Twelve newly diagnosed NPC patients treated by intensity-modulated radiation therapy(IMRT) were enrolled in the study. Positioning should be aligned both with isocenter and ASM lines at odd number of times, while only with isocenter at even number of times. Through cone beam computed tomography(CBCT) scans and image registration, the translational errors of X, Y, Z and the rotational errors of Rx, Ry, Rz were recorded respectively. Results The translational errors of X, Y, Z were(0.14±0.14) cm,(0.16±0.10) cm,(0.14±0.11) cm by ASM and(0.16±0.12) cm,(0.17±0.10) cm,(0.14±0.10) cm by single isocenter method(SIM), respectively, with statistically significant difference in X direction between two methods(HR=0.044). The rotational errors of Rx, Ry and Rz were(0.35°±0.33°),(0.77°±0.64°),(0.44°±0.42°) by ASM and(0.41°±0.36°),(0.92°±0.63°),(0.74°±0.52°) by SIM, respectively. The differences in Ry and Rz between two method were statistically significant(HR=0.006, 0.000). Conclusion Using ASM, the translational errors of X axis, and the rotational errors of Ry and Rz can be effectively reduced for NPC patients during daily positioning in IMRT, which is worthy of application in the clinical practice.