This study attempts to assess the effect of the 1st class health insurance program to the income redistribution among the participants in a unit health insurance cooperative. One health insurance cooperative, located in Seoul, with 1558 members and 768 households was selected for this purpose. The relationships between amount of premium payed and benefits from the cooperative were compared. Necessary data were obtained from the bills submitted to the health insurance cooperative by the contracted medical institutions from 1st January 1977 to 30th June 1979. Households and individuals were the unit of the assessment. The indicators measuring income redistribution effect were the ratios between the benefit and expected benefit and the ratios between the benefit and the mean benefit. The major findings were: 1. The ratios between the benefits and the expected benefits were lower than 1 in the high income group and greater than 1 in the middle and lower income groups. This fact imply that the income redistribution effect was shown in the studied groups. It was shown that the middle income group received the greatest benefit, and then the lower income group. 2. The ratios between the benefit ana the mean benefit of the households in the higher standard income grade, were found to be higher. This means that the equity of the benefits of households were not achieved by the policy of the health insurance plan. 3. The health insurance utilization rates of the higher standard income group, measured by the household unit, were higher, and by the individual unit, the same rates of the middle income group were higher than other groups.