This thesis reports the findings of an experimental study on the interpretation of subject pronouns in Croatian monolingual children aged 4-6 years. Croatian is a pro-drop language, which means that it allows for the subject pronouns to be realized overtly (these are the so-called overt pronouns) or to remain phonetically empty (these are the so-called null pronouns). Because the mastery of subject pronouns relies on both morphosyntactic and discourse-pragmatic knowledge, their acquisition may prove to be a difficult process. The task used to test children’s interpretation of null and overt subject pronouns was a picture selection task. The participants were presented with two pictures and had to choose the one which corresponded to the meaning of the sentence presented orally. The sentences consisted of a main and a subordinate clause. Main clauses contained a noun acting as the subject and a noun acting as the object, while subordinate clauses contained either a null or an overt pronoun. The pronouns were ambiguous as both nouns, matched in gender, number and animacy, could be linked to them. The results showed that 4-, 5- and 6-year-olds differed from adults in their interpretation of both null and overt subject pronouns. The responses of all groups of children in the null pronoun condition were split between the main clause subject and the main clause object, and differed statistically from those of adults, which demonstrated a bias, albeit weak, towards the main clause subject. With regard to the overt pronoun condition, children aged 5 and 6 years demonstrated a bias towards the main clause object as the antecedent, although statistically not as strongly as adults. From the statistical point of view, the responses of all groups of children differed from adults’ in this condition. Overall, the results suggest that adult-like antecedent preferences with null and overt subject pronouns develop past the age of 6 in Croatian monolingual children, although some preliminary signs of this development are already present at the age of 5.