We have investigated the optical and structural qualities of InxGa1-xN/InyGa1-yN multi-quantum wells (MQWs) on sapphire substrates using atomic force microscope (AFM), high resolution X-ray diffraction (HRXRD), and photoluminescence (PL). In0.08Ga0.92N/ In0.02Ga0.98N five MQWs were grown by metalorganic chemical vapor deposition with three different well growth rates. We found from HRXRD and AFM that the interface roughness of MQWs was improved and the density of threading dislocation with screw component was decreased from 1.2 x 10(9)/cm(2) to 2.5 x 10(7)/cm(2) with decreasing the growth rate. Moreover, PL measurements revealed that the MQWs grown with a lower growth rate represented higher PL intensity, narrower line width and less energy shift in power dependent PL. This implies that lower growth rate allows adatoms on the surface to have longer time to arrive at two-dimensional step ledges of growth front and thereby enhances crystal quality compared with higher growth rate, leading to enhanced optical and crystal quality of MQWs. (C) 2002 Elsevier Science B.V. All rights reserved.