Ionic amphiphilic diblock copolymers, such as polystyrene-b-poly(styrenesulfonate), show non-surface activity when some requirements are satisfied. The main origin of this unique property has been thought to be an image charge repulsion at the air/water interface. In this study, surface activity/non-activity was examined for random copolymers in addition to homopolymers. Random copolymers of styrene and styrenesulfonate were found to be surface active, while the poly(styrenesulfonate) homopolymer was slightly surface active. This observation cannot be interpreted by image charge repulsion alone since these are all polyanions and the block copolymer is mostly hydrophobic. Stable polymer micelle formation in the block copolymer system is also an essential origin of non-surface activity.