Here, we have successfully fabricated high performance mainspring by co-electrodeposition of functionalized multi-walled carbon nanotubes coating in the presence of chitosan. The functionalized multi-walled carbon nanotubes (f-MWCNTs) can be easily electro-deposited with chitosan onto the mainspring under a moderate condition, with controllable film thickness from a few hundred nanometers to tens of micrometers. The Young modulus of the coated mainspring was evaluated by a cantilever loading test. Our results show that the Young modulus of a mainspring coated with a f-MWCNT composite layer has been greatly improved. A 5 pm composite coating on a 100 mum mainspring (implying a 5 increase in the total thickness) can increase the Young modulus, by an average of 41.6%. The reported co-electrodeposition technique provides a facile approach to form stable, reproducible, and rigid f-MWCNTs composite coating, which leads to realization of high-performance mainspring with reinforced mechanical strength.