The effect of fertility on female labor supply decisions in Turkey is analyzed in this thesis. Taking the endogeneity between fertility and labor supply into account, the causal effect of fertility is interpreted in an instrumental variables estimation framework. Results of the analysis indicate that fertility estimates of sex preference and twin based instruments on short term labor supply of women differ substantially. While fertility increases due to sex preference instrument cause no significant change in labor supply decisions, unexpected fertility shocks by twin instrument have an adverse effect on female labor supply.