**Abstract** Previous cross-linguistic studies have shown that object relative clauses (ORCs) are typically harder to parse than subject relative clauses (SRCs). The cause of difficulty, however, is still under debate, both in the adult and in the developmental literature. The present study investigates the on-line processing of SRCs and ORCs in Greek-speaking 11- to 12-year-old children and adults, and provides evidence on relative clause processing in Greek—a free word order language. We conducted a self-paced listening task in which we manipulated the type of relative clause (SRC vs. ORC), the RC internal word order (canonical vs. scrambled), and the type of relativizer (relative pronoun vs. complementizer). The results showed that SRCs were overall processed faster than ORCs, providing evidence that children follow similar processing strategies to adults. In addition, accusative case marking facilitated the processing of non-canonical structures in adults but less so in children. Children showed heavy reliance on word order, as they processed nominative and accusative pre-verbal NPs in exactly the same way, while they were strongly garden-pathed in ORCs with post-verbal nominative NPs. We argue that these results are compatible with the Competition Model.