As a critical closure equation to the two-fluid model and an important tool to characterize the two-phase flow interfacial transport, interfacial area transport equation (IATE) was formulated by taking various physical mechanisms causing interface area change into account. To fulfill the dynamic prediction advantage of the IATE and further replace the flow-regime-based constitutive relations, the IATE model should be validated by transition data to ensure the model reliability and robustness. Air-water experiments are performed in bubbly to slug transitions flows in a 200×10 mm narrow rectangular duct. Four-sensor conductivity probes are used to measure the local void fraction, interfacial area concentration, and bubble velocity at three axial locations. The sectional void fraction distribution changes significantly with the flow developing. Flow conditions with similar area-averaged void fraction but different superficial mixture velocities are compared, and it is found that the superficial liquid velocity obviously affect the interfacial area concentration. The measured data with developing spatial distribution would be useful to benchmark and improve the current two-phase flow models used in CFD. Besides, the two-group IATE model for narrow rectangular channel is evaluated using the collected data. The average relative error for the interfacial area concentration prediction is 11.4%, but the group II IAC are overestimated for most flow conditions. To realize better prediction in bubbly to slug transition flows, improvement of the current IATE model is required.