The purpose of this study was to explore effects of physical fitness, sports activities and aging on low-back pain (LBP). The subjects (age: 20-62 years) were two hundred six women who worked at a nursing home. They performed a physical fitness test which consisted of anthropometry (height and weight), muscle strength (grip, trunk extension, trunk flexion and knee extension), trunk flexibility (flexion and extension), balance (one leg standing with eyes open and eyes closed), and 1Om-walking at maximum speed(velocity, step length, and cadence). All variables in the physical fitness test except weight decreased with aging. A factor analysis with a Varimax rotation revealed four interpretable factors; STRENGTH, WALKING, FLEXIBILITY and BALANCE. The subjects answered a questionnaire on experience of LBP, sports activity, and an exercise for preventing LBP. The past and/or present experience of LBP increased with aging; 64.9% in 20-39, 71.2% in 40-49 and 75.9% in 50-59 age group. A path analysis was applied to a model, whereby four physical fitness factor scores, age, sports activities and the exercise for preventing LBP (EXERCISE) were assumed to effect on the LBP experience. The path analysis indicated that STRENGTH, FLEXIBILITY and EXERCISE had direct effects on LBP, while aging, sports activities, and EXERCISE related to the LBP experience indirectly through STRENGTH and FLEXIBILITY. This study supported the hypothesis that the experience of LBP was affected by muscle weakness and a limit in trunk flexibility which were dependent on aging and sports activities. The contribution of these factors to the LBP was small(7%), suggesting many other causes of LBP.