Multipass friction stir processing of Fe based metallic glass ribbons interspersed between Cu plates was performed. From the first pass, the process entailed on the one hand the decrease of the Cu mean grain size in the nugget by a factor of about 5 and on the other hand the fracture, the refinement and the partial crystallization of the amorphous reinforcement. Cu diffusion also led to marked Cu enrichments in the Fe based metallic glass whose mean Cu content reached 2.7 at%. Beside the metallic glass based reinforcements, some nanometric polycrystalline copper oxides were formed and dispersed within the nugget. The nugget also experienced dynamic recovery and dynamic recrystallization which was in particular favored by the accumulation of dislocations around the reinforcements. Finally, the greater number of passes, the harder the nugget becomes.