Did homo erects have smaller brains than Australopithecus?

No, Homo erectus had larger brains than Australopithecus. Homo erectus had an average brain size of around 900 cubic centimeters, while Australopithecus had a brain size of around 400-500 cubic centimeters. This increase in brain size is thought to be one of the key factors in the evolution of Homo erectus.