Introduction: The radiographic classification for developmental dysplasia of hip to quantify the severity of disease consist of Tonnis and International Hip Dysplasia Institute (IHDI) classification. The Ossification center of the femoral head in DDH patient more than six months is still vague or eccentric, so the reliability of both classifications is still in question and especially is influenced by the experience of the observer. This study aims to test and compare interobserver reliability in evaluation of DDH patients using IHDI and Tonnis classification assessed by senior and junior orthopaedic residents which had different degree of experience. Materials and Methods: This study used retrospective analysis of pelvic supine AP view radiograph of DDH patients from 2014 to 2017. All three observer groups analysed the pelvis radiographs using Tonnis and IHDI classification. Inter and intra-observer reliability was measured by Cohen’s and Fleiss Kappa method, respectively. Results:The Fleiss Kappa value for 15 radiographs of DDH patients assessed by senior residents using Tonnis and IHDI classification are 0.715 and 0.832 and result of Fleiss Kappa value assessed by junior residents are 0.577 and 0.845, respectively. Intra-observer reliability for Tonnis classification was lower in junior group compared to other two groups but showed almost perfect value in all groups for IHDI classification. Conclusion: Significantly different results were noted between junior and senior residents in assessing DDH severity, with higher diagnostic reliability in senior residents compared to junior residents. In general, junior resident has less clinical experiences in many aspects in comparison with the seniors.