Tribological properties for unlubricated sliding wear of electroless Ni-P/diamond composite films with different ceramic contents were evaluated by the pin-on-disk method with different applied loads with Al2O3 countermaterial. As-plated amorphous and heat-treated crystalline matrices were considered. Hardness, Young modulus, Milman plasticity parameter, and crack-arrest fracture toughness were evaluated by diamond pyramid indentation methods. Correlations among mechanical properties and tribological behavior were evaluated quantitatively. The wear resistance of as-plated samples with an amorphous matrix can be correlated with hardness. The wear resistance of heat-treated samples with crystalline two-phase matrix can be correlated with fracture toughness.