A duct is an enclosed passage for transmission of a substance, especially liquid or gas with extensive usage in heating, ventilation, and air conditioning (HVAC) applications and gas industries. Practically, duct shapes have deviations from ideal geometric shapes, predominantly in thin-walled structures due to joint conditions. The aim of the present research is to understand the effect of duct joints on modal parameters. In this study, Experimental Modal Analysis (EMA) is carried out on three different rectangular ducts having different joints and materials. Numerical Modal Analysis (NMA) is then performed on these ducts by modelling the corresponding joints. The Modal Assurance Criteria (MAC), frequency comparison, and auto-MAC plots are used to check the correlation between the experimental and numerical results. Based on these comparisons, a good match in natural frequencies but a mismatch in mode shapes are observed. © 2018 International Institute of Acoustics and Vibrations. All Rights Reserved.