The purpose of this study was to investigate the time dependent effects among factors affecting duration of work disability after compensated low-back pain. A postal survey involving 238 compensated workers at 39 companies was performed between January 5, 2004, and March 23, 2004. Cox proportional hazard regression analysis was used to model the effect of demographic, work-related, and injury factors affecting the duration of work disability. The variables that significantly affected the duration of work disability were age, company size, compensation benefit, pain radiation, and diagnosis. In addition, company size and pain radiation showed statistically significant time dependent effect. Consequently, this study found that there were time dependent factors affecting the duration of work disability. A phase-specific analysis would be useful to make policy for the prevention of long term disability after back injury.