Graphene/polyaniline (GN/PANI) composites were synthesized by in situ polymerization with the assistance of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123). We show that the addition of P123 enhanced the wettability of GN and hence improved its uniformity in aqueous solution and the dispersity of PANI loaded on GN surface. Structural and morphological analyses indicate that GN has been successfully coated with PANI. P123 was mainly acted as soft temples to improve the control of morphology and increase composites effective specific surface area. Furthermore, it can improve composites capacitive performance as evidenced by electrochemical tests. When the molar ratio of P123 to ANI is 0.0108, the composites exhibit the best performance, in terms of the rate capability, the lowest equivalent series resistance (0.31 Omega) and the charge-transfer resistance (1.46 Omega). Additionally, it achieves a capacity retention of 91.8 % after 1000 charge-discharge cycles at the current density of 500 mA g(-1), an increase of 82 % over the composites without P123. A mechanism for interactions of P123, GN, and PANI is proposed in this work.