Epitaxial SrTiO3 films were fabricated by laser molecular beam epitaxy on bare and TiO2 buffered GaN(0002), respectively. The whole deposition processes were in situ monitored by reflection high energy electron diffraction (RHEED). X-ray diffraction (XRD) was carried out to study the growth orientation and crystalline quality of STO films. The interfacial characters and epitaxial relationships were also investigated by high revolution transition electron microscope and selected area electron diffraction (SAED). According to the RHEED observation, the lowest epitaxy temperature of STO on TiO2 buffered GaN was decreased compared with the direct deposited one. The epitaxial relationship was (111)STO//(0002)GaN in both cases as confirmed by RHEED, XRD, and SAED. The full width at half maximum of ω-scan and Φ-scan of STO on TiO2 buffered GaN was reduced compared with that deposited on bare GaN, indicating that epitaxial quality of STO film is improved by inserting TiO2 layer. In summary, the lattice mismatch was reduced by inserting rutile TiO2. As a result, the crystalline temperature was reduced and enhanced epitaxial quality of STO thin film was obtained.