In this work, we report the formation of a supramolecular assembly of graphene with a donor-π-acceptor (D-π-A) molecule to detect low concentration NO2. 5-Aminonaphthalene-1-sulfonic acid (ANS) was used herein to π-π stack with reduced graphene oxide (rGO), the resulting π-conjugated bridge being linked by a donor unit (-NH2) and an acceptor unit (-SO3H). The prepared ANS-rGO shows the highest response (Ra/Rg = 13.2 to 10 ppm NO2) so far among the reported organic molecule modified graphene materials, and excellent selectivity and reliable reversibility at room temperature. Furthermore, as revealed through the charge density difference calculation, it is the effective enhancement of charge transfer between ANS and graphene that should be responsible for the sharp improvement of NO2 gas response of the material. Thus, for the first time, we demonstrate that supramolecular assembly of a D-π-A molecule and graphene provides a facile and effective approach to fabrication of high performance graphene-based gas sensors.