Owing to the quite similar chemical properties of H2 O and D2 O, rational molecular design of D2 O optical sensors has not been realized so far. Now purely organic chromophores bearing OH groups with appropriate pKa values are shown to display distinctly different optical responding properties toward D2 O and H2 O owing to the slight difference in acidity between D2 O and H2 O. This discovery is a new and facile strategy for the construction of D2 O optical sensors. Through this strategy, ratiometric colorimetric D2 O sensor of NIM-2F and colorimetric/fluorescent dual-channel D2 O sensor of AF were acquired successfully. Both NIM-2F and AF can not only qualitatively distinguish D2 O from H2 O by the naked eye, but also quantitatively detect the H2 O content in D2 O.