The off-stoichiometric La1.2Fe11.6Si1.4B0.75 alloys with different solidification rate were prepared by the arc-melting and melt-spinning methods, and the microstructure, magnetic and magnetocaloric properties of the annealed samples were investigated. It is found that the extra La and refined microstructure (induced by rapid cooling technique) shortened the annealing time to 30 min at 1273 K. The B atoms partially dissolved in lattice interstice of 1:13 phase and brings about the lattice expansion, which improves the TC and enhances the MCE of the La1.2Fe11.6Si1.4B0.75 alloy. The high cooling rate contributes to the depression of thermal and magnetic hysteresis. In the annealed La1.2Fe11.6Si1.4B0.75 ribbon with wheel speed of 10 m/s, the mass fraction of 1:13 phase is 86.8 wt%, and a large maximum magnetic entropy change of 20.2 J·kg−1K−1 with small thermal and magnetic hysteresis can be obtained at 193 K under field change of 2 T.