A forging alloy for manufacturing a golf club head is a stainless steel alloy including carbon 0.08-0.16 wt %, silicon <0.8 wt %, manganese <1.0 wt %, chromium 11.5-17.0 wt %, with the remaining portion being iron. When the forging temperature of the stainless steel alloy is below a transition temperature of a delta ferrite phase thereof, the stainless steel alloy can be subjected to warm forging in a smooth manner at a temperature of 720-960 .degree. C. and an operational force of 580-860 ton. Thus, a highly rust-resisting and highly wear-resistant golf club head can be manufactured.