In this study, the effects of job characteristics of middle-aged workers on job and life satisfaction were examined, and furthermore, the mediating effects of subjective class identification were verified in the relationship between job characteristics and job/life satisfaction. For this purpose, the survey of 1,317 middle-aged workers was conducted by the Korean Logitudinal Study of Aging 2008. The results of this study showed that working conditions(job status, monthly average wage, regularity of working hours), work characteristics(physical and office duties), and organizational environment had significant effects on job satisfaction. Also, job characteristics with monthly average wage, regularity of working hours, and work characteristics of office jobs had a significant effect on life satisfaction. Furthermore, the mediating effect of subjective class identification in the relationship between job characteristics and job/life satisfaction of middle-aged workers was statistically significant in the relationship between variables except for work type and organizational envrionment. Based on the results of this study, we discussed the quality of jobs for middle-aged workers and the ways to improve the workplace environment.