The effect of well number in 1.3 µm GaInAsP Graded-Index Separate-Confinement-Heterostructure Multiple-Quantum-Well (GRIN-SCH-MQW) laser diodes (LDs) is examined experimentally in terms of threshold current density Jth, differential quantum efficiency ηd and internal loss α. For LDs with cavity length L of 270 µm, Jth as low as 0.9 KA/cm2 was obtained with 5 quantum wells. ηd as high as 81% and α as low as 5 cm-1 were obtained with 4 quantum wells. Taking these parameters into account, 4 or 5 is calulated to be the optimum number of quantum wells for the present structure, which was confirmed experimentally. Light output power of 56 mW/facet with a narrow and circular output beam was obtained in a buried heterostructure (BH) GRIN-SCH-MQW LD entirely grown by Metalorganic Chemical Vapor Deposition (MOCVD). These results indicate that the use of a GRIN-SCH in a MQW LD of the GaInAsP/InP system is effective in the improvement of laser characteristics.