The microstructure evolution and the mechanism of the formation of NaZn13-type 1:13 phase of La0.6Pr0.5Fe11.4Si1.6 alloys during annealing were investigated. After annealing at 1373 K for a proper period of time (15days for the bulk alloy and 4 hours for melt-spun ribbons), almost pure 1:13 phase was obtained. But with an overlong annealing time, 1:13 phase began to decompose and macroscopic α-Fe dendrites and La-rich phases appeared. Magnetocaloric effect of both La0.6Pr0.5Fe11.4Si1.6 bulks and melt-spun ribbons were also systematically studied. It was found that bulk sample exhibited larger thermal and magnetic hysteresis losses as a result of the stronger first-order transition, yet still showed higher magnetic entropy change and refrigerant capacity than those of melt-spun ribbons. By applying a field of 0–5 T, the magnetic entropy change and effective refrigerant capacity for bulk sample were 25.2 J/ (kg·K) and 474.1 J/kg, while those of melt-spun ribbons turned out to be 21.9 J/ (kg·K) and 458.5 J/kg.