The objective of this study was to investigate socioeconomic inequalities in work ability among municipal employees and the contribution of work conditions to these inequalities.The subjects were employees of the City of Helsinki and were all over 40 years of age. Data (N=1,827) were collected in the age-group-based medical check-ups by occupational health personnel. Work ability was measured with a work ability index. The association between the work ability index with socioeconomic status was examined by fitting logistic regression models.There was a consistent gradient in work ability, lower socioeconomic groups having poorer work ability. Adjusting for physical stress accounted for a substantial part of the socioeconomic inequalities. Adjusting for possibilities for influence and development at work accounted for some of the difference between white-collar and blue-collar employees, but not for differences between the white-collar subgroups among the women. Mental stress and problems in the social environment were not clearly associated with the inequalities.Socioeconomic inequalities in work ability among municipal employees correspond to the inequalities in ill health found in general populations. Physical stress at work explained a large part of the inequality. Poor possibilities to influence one's work contributed to the excess of lowered work ability among the blue-collar employees, but not to the inequalities between white-collar subgroups of women. Apart from physical workload, work conditions did not explain socioeconomic inequalities between white-collar subgroups of women.