Nickel particles dispersed in an amorphous carbon matrix have been synthesized by a sonication method, and further heated at 773 K under Ar atmosphere. Both as-prepared and heated samples have been fully characterised using different techniques such as transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy dispersive X-ray analysis (EDX), X-ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS) and energy filtered TEM (EFTEM). The as-prepared sample shows amorphous spherical particles formed by Ni2+ dispersed in a carbon matrix. After heating, the formation of small metallic nickel nanocrystallites inside these spherical particles is observed. The EELS spectra show a decreased oxygen content in the heated sample due to the reduction of Ni2+ in the presence of carbon. This result is also confirmed by XAS. In addition, the EELS and EFTEM analyses indicate that the nickel nanocrystallites are surrounded by amorphous carbon which provides some protection to the metallic nickel from oxidation.