Effect of hydroxyapatite (HAP) without graphene oxide (GO) and graphene oxide/hydroxyapatite composite (GO/HAP) containing 0.1% mass fraction of GO on in vitro remineralization of acid-etched bovine enamel was investigated. The surface and cross-section morphology, surface element, crystal structure and mechanical properties of the bovine enamel before and after remineralization were characterized by field emission scanning electron microscopy, EDX spectroscopy, X-ray diffractometer and Vickers microhardness tester. The results show that the GO/HAP composite form flower-like crystals with weak binding force on the surface of the acid-etched enamel. After ultrasonic stripping of these crystals, the demineralized enamel surface and the inter-rod gap are well repaired. The cross-section morphology shows that the GO/HAP composite can repair the deep enamel demineralization, promote the formation of a large number of tiny crystals between the enamel prisms, and the formation of order arranged crystals in the demineralized inter-rod gap. At the same time, the surface Ca/P molar ratio and crystal composition of the acid-etched enamel are well restored after the GO/HAP treatment.