The optical and crystal properties of InGaN/GaN multiple quantum wells (MQWs) grown by MOVPE were characterized using room-temperature photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD), respectively. The emission wavelength showed a blueshift with higher growth temperature as well as lower ammonia flow rate. The emission intensity of PL increased with increasing the number of InGaN/GaN MQW pairs, however, the full width at half maximum (FWHM) of band-edge emission was degraded. Not only was the indium mole fraction determined, but the abrupt interfaces between wells and barriers were observed from HRXRD measurement results. These results suggests that one can improve the optical and crystal qualities of InGaN/GaN MQWs by optimizing the growth temperature, ammonia flow rate and the number of the MQW pairs for the blue laser diode applications. (c) 2006 Elsevier B.V. All rights reserved.