We examined the relationship among riboflavin intake, work activity, erythrocyte glutathione reductase activity coefficient(EGR AC)and urinary riboflavin excretion. We also attempted to determine factors affecting seasonal riboflavin status of rural women. All information about nutrient intake, work activity and riboflavin biochemical status was repeatly collected in three seasons ; farming season(June), harvest season(October), nonfarming season(February). EGR AC was negatively correlated with riboflavin intake(P<0.005) and positively correlated with the duration(min) of farming activity(P<0.005) and the percentage of lean body mass(LBM) (%) representing long term physical activity(P<0.05) in harvestseason. Urinary riboflavin excretion was positively correlated with the ratio of riboflavin intake to 1,000kcal of energy expenditure (P<0.05) in farming season and negatively correlated with the duration(min) of farming activity (P<0.05) and crude nitrogen balance(P<0.005) in harvest season. It appeared that EGR AC seems to increase and urinary riboflavin excretion seems to decrease as work activity increase. Therefore work activity would be expected to deteriorate riboflavin status. Multiple regression analysis of variables showed that in general EGR AC was affected by riboflavin and energy intakes, energy expenditure, energy balance, the duration(min) of farming activity, LBM (%). Urinary riboflavin excretion was affected by riboflavin and protein intakes, LBM(kg) and crude nitrogen balance. Crude nitrogen balance affected urinary riboflavin excretion in all seasons. The result indicated that work activity as well as nutrient intake seemed to affect riboflavin status, especially EGR AC was affected preferentially be work activity in all seasons.