Objective: In this study, the comprehension of subject-subject (S-S) and subject-object (S-O) relative clauses was compared between children with cochlear implants (CI) and normally-hearing (NH) ones, and three types of errors were analyzed in order to improve the comprehension of these relative clauses. Finally, the comprehension of these clauses was compared. Method: In order to evaluate the comprehension of S-S and S-O relative clauses, a picture-matching test with four alternatives was designed. One of the alternatives was the correct response and the other three were main clause error (MCE), relative clause rrror (RCE), and double clause error (DCE). Data were analyzed using Mann-Whitney U test in SPSS 22. Result: Results demonstrated significant differences between CI and NH groups in the comprehension of both types of relative clauses (p=0.006). Moreover, children with CI encountered more difficulties in the comprehension of S-O relative clauses, and the percentage of all three types of errors increased in them. Conclusion: Chidren with CI fail to comprehend only one part of relative clauses. Furthermore, in S-S relative clauses, the most common error is related to MCE, indicating that these children cannot comprehend the relationship between subjects and verbs in main clauses. The percentage of all errors in S-O relative clauses is increased in this group and the comprehension of this type of relative clause is more difficult for them. The noted problems may be eliminated with further and earlier training for children with CI.