Recent models on parenting propose different roles for fathers and mothers in the development of child anxiety. Specifically, it is suggested that fathers' challenging parenting behavior, in which the child is playfully encouraged to push her limits, buffers against child anxiety. In this longitudinal study, we explored whether the effect of challenging parenting on children's social anxiety differed between fathers and mothers. Fathers and mothers from 94 families were separately observed with their two children (44 % girls), aged 2 and 4 years at Time 1, in three structured situations involving one puzzle task and two games. Overinvolved and challenging parenting behavior were coded. Child social anxiety was measured by observing the child's response to a stranger at Time 1, and half a year later at Time 2, and by parental ratings. In line with predictions, father's challenging parenting behavior predicted less subsequent observed social anxiety of the 4-year-old child. Mothers' challenging behavior, however, predicted more observed social anxiety of the 4-year-old. Parents' overinvolvement at Time 1 did not predict change in observed social anxiety of the 4-year-old child. For the 2-year-old child, maternal and paternal parenting behavior did not predict subsequent social anxiety, but early social anxiety marginally did. Parent-rated social anxiety was predicted by previous parental ratings of social anxiety, and not by parenting behavior. Challenging parenting behavior appears to have favorable effects on observed 4-year-old's social anxiety when displayed by the father. Challenging parenting behavior emerges as an important focus for future research and interventions.