Objective: The purpose of this study was to investigate the outcomes of adding lumbar sustained natural apophyseal glide (SNAG) to a conventional therapy program for chronic nonspecific low back pain (LBP). Methods: Forty-two participants with chronic nonspecific LBP were randomly divided into 2 groups. The study group (aged 27.1 ± 8.3, 20 men, 3 women) received a conventional physical therapy program consisted of stretching and strengthening exercises plus SNAG (based on the Mulligan concept) on the affected lumbar levels, and the control group (aged 28.9 ± 7.7, 13 men, 6 women) received the same conventional program without SNAG 3 times per week for 1 month. Outcome measures were repositioning error (the primary outcome), pain, and function measured by an isokinetic dynamometer, visual analog scale, and the Oswestry Disability Index. Measurements were recorded before and after the end of the treatment period. Results: The comparison between pretreatment and posttreatment test scores indicated that both study and control groups had significant improvement in all dependent variables (P N .001). However, adding SNAG to the conventional program resulted in higher improvement in terms of repositioning error, pain, and function (P = .02, .002, .008) respectively. Conclusions: This preliminary study indicated improvement in both groups. Adding SNAG to conventional programs in the treatment of chronic nonspecific LBP may result in greater improvement of repositioning error, pain reduction, and improved function. (J Chiropr Med 2017;16:94-102)