Significant technical and optical advancements are required for intraoperative optical coherence tomography (OCT) to perform boundless surgical applications in otology, since the translation of OCT for surgical-microscope facilitates the simultaneous OCT and microscopic visualization of soft tissue structures of the surgical region with a high-resolution in real-time. Herein, we developed an augmented-reality intrasurgical OCT microscope system with an extended 280 mm working distance, which simply provides a sufficient space for the manipulation during surgeries compared to conventional techniques. Ex vivo experiments were initially performed to evaluate the enhanced system performances and secondly, the developed system was well-utilized to clinically assess the preliminary findings of tympanomastoidectomy in six patients with chronic otitis media. The OCT system evaluated the residual inflammation of region of interest in the mastoid bone and most importantly OCT was sufficiently useful for visualizing the connection between the graft and remnant tympanic membrane intraoperatively. Use of this extended-working distance OCT integrated surgical-microscope enables the surgeons to precisely define the aforementioned surgical requirements, while performing intraoperative imaging over the complete range.