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The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) grown on sapphire by metalorganic chemical vapor deposition (MOCVD) have been investigated by optical measurements of temperature-dependent photoluminescence (PL), photoluminescence excitation (PLE) and time-resolved photoluminescence (TRPL), and structural analysis methods of high-resolution X-ray diffraction (HRXRD) and high-resolution transmission electron microscopy (HRTEM). Two typical samples are studied, both consisting of five periods of InGaN wells with 1.6 nm thickness with different indium compositions of 21 and 24%, respectively. The thickness of the GaN barrier was 7.9 nm. According to the PL and PLE measurement results, large values of activation energy and Stokes' shift are obtained. This indicates that higher In composition results in the increase of composition fluctuation in the InGaN MQW region, showing the stronger carrier localization effect. The lifetime at the low-energy side of the InGaN peaks is longer for higher indium composition, as expected from the larger Stokes shift.