Provided are: an active material composite powder which is capable of reducing resistance; and a method for producing the active material composite powder. This active material composite powder contains an active material and lithium niobate adhered to the surface of the active material, and has a BET specific surface area (S [m2/g]) satisfying 0.93 < S < 1.44. This method for producing an active material composite powder comprises: a spray drying step wherein a solution containing lithium and a peroxo complex of niobium is sprayed onto an active material and dried thereon in parallel; and a heat treatment step wherein a heat treatment is carried out after the spray drying step. The temperature of the heat treatment is more than 123 DEG C but less than 350 DEG C.