This paper proposes a graphene-oxide-enhanced surface plasmon resonance (SPR) sensor based on side-polished fiber. A silver film is deposited to excite the surface plasmon wave. Seldom graphene oxide nano-films are then decorated on the silver surface of the sensor, where self-assembly octadecanethiol films serve as a link between graphene oxide and silver. The decorated composite films protect the silver film from degradation and enhance the sensor's stability. Compared with the same SPR sensor without graphene-oxide decoration, the average sensitivity of the proposed SPR sensor is 2252.5 nm/RIU in the test range of 1.32-1.34 RIU (RIU is refractive index unit), which is enhanced by 1.48 times, and the figure of merit is comparable with the former without any significant decrease due to the increase of film layers. The proposed fiber sensor is a promising candidate in applications such as antibody antigen immunoassays with high immobilization ability.