Purpose: The purpose of this study was to identify the factors influencing parenting stress in primiparas. Method: The participants in this study were 198 primiparas of infants aged 1-6 months who visited well baby clinics in 5 hospitals. The data were collected from April 15 to June 15, 2003. Results: The mean score for parenting stress was 2.4 of a possible 5 and thus considered average. The score for parenting stress was significantly correlated with the level of maternal perception of the infant and the level of social support. The score for parenting stress was significantly different according to the education level of the primiparas and prenatal management. For the primiparas, social support($20\%$) and maternal perception of the infant($9\%$) were significant predictors explaining parenting stress. Conclusions: Nursing interventions to improve maternal perception of the infant and increase social support should be provided for primiparas in order to reduce parenting stress.