This paper studies the pattern of labour supply of Japanese married women. The study develops and tests a discrete work choice model with a differing level of fixed cost of work and equalizing wage differentials. This accounts for differences in work characteristics of the regular status and part-time status work at firms, the family and self-employment. A 20 to 30 per cent hourly wage differential was observed between work categories with control on skills, region and other variables. Different effects are studied of the number and ages of children, a grandmother's presence and the wife's educational attainments on the category of work selected.The data employed come from The Occupational History and Mobility Survey of Women 1983 (OHMS), conducted by the National Institute for Vocational and Occupational Research, and allow detailed wage regression and consideration of different work categories which were not feasible in previous works. Empirical regularities of the Japanese labour market, such as the absence of growth in labour participation for mothers with small children, are better explained when work categories are dealt with separately.