The "Non-Surface Active Amphiphilic Diblock Copolymer" is a novel class of molecules which is contradict with the "common sense" of the surface and interface science. They are certainly amphiphilic so they form micelles in aqueous media when dissolved. However, they do not adsorb onto the air/water interface. Hence, the surface tension of the solution does not decrease with polymer concentration and the solutions show very less foam formation activity. This curious molecule is in principle ionic amphiphilic diblock copolymers, which consist of polyelectrolyte and hydrophobic chains. The origin of this "curious phenomenon" is thought be the balance of image charge repulsion at the air/water interface and hydrophobic adsorption force. In addition, the "polymerity" was found to be an important factor: the block copolymer m:n=64:53 (poly(stynrene)-b-poly(styrene sulfonate)) showed non-surface activity but that with m:n=18:18 showed very high surface activity, although the block ratio is almost 1:1 for both of these polymers. The (poly(fluorinated styrene)-b-poly(styrene sulfonate)) with m:n=30:64 showed non-surface activity but that with m:n=11:64 showed surface activity. Hence, it can be concluded that the minimum length exists for appearance of non-surface activity, which might be around m=30 for hydrophobic chain and n=50 for ionic chain. The effect of hydrophobicity of the hydrophobic chains on the non-surface active nature was also investigated. Unexpectedly, the non-surface activity was in the order of poly(n-butylacrylate) < poly(styrene) < poly(fluorinated styrene) as the hydrophobic chain with same ionic block, although the hydrophobicity is higher in this order. Ref. P.Kaewsaiha, et al., Langmuir, 21(22), 9938 (2005).