A novel method to combine hot pressing and grain boundary diffusion in order to fabricate La(Fe,Si)13 based magnetocaloric composites is described. LaFe11.6Si1.4/La-Co magnetocaloric composites were prepared by hot-pressing, followed by diffusion annealing heat treatment. The Curie temperature (TC) of these composites increases from 197 K to ∼235 K due to the diffusion of Co into the NaZn13–type (1:13) majority phase. The maximum magnetic entropy change (–ΔSM)max at 2 T first increases with increasing diffusion time from 5.62 to 7.60 J/(kgˑK) and followed by a further increase up to 9.15 J/(kgˑK) due to the recombination of the 1:13 phase. The Co content of the La-Co binder could be used to tune the formation of the desired 1:13 phase. •LaFe11.6Si1.4/La-Co composites were prepared by hot-pressing followed by diffusion annealing.•The diffusion of Co into the NaZn13–type majority phase can improve the TC of these composites.•Improvement in the MCE of these composites is due to the recombination of 1:13 phase.•HP and GBD can be used in mass production of high performance La(Fe,Si)13 based MCMs.