The phase diagram obtained for Nd0.5 Ca0.5-y Sry MnO3 from the temperature dependent magnetization and electron spin resonance measurements are presented in this paper. It is found from magnetization measurements that y=0.25 is a critical point where a magnetic transformation occurs, accompanied by a nonmonotonic variation in the c lattice parameter. Below a certain transition temperature, compounds with y<0.25 exhibit charge ordering and those with y0.25 show ferromagnetic ordering. An antiferromagnetic transition occurs for y=0 at still lower temperatures whereas a phase separation into antiferromagnetically and ferromagnetically ordered states occurs for 0<y0.5. Electron spin resonance analysis shows that the phase separation occurs at temperatures above the ferromagnetic transition temperature in all the compounds with y>0.