Objectives: To address the challenge of observing the round window niche during exoscopic cochlear implantation, an assisted endoscopic underwater drilling technique was developed. Methods: To improve visibility, we introduced an endoscopic underwater technique after posterior tympanotomy for enhanced visualization of round window area. The procedure transitions between the exoscope and endoscope, with saline irrigation clearing bone dust and blood. Results: Operation times were slight longer, but it offered enhanced safety and ergonomic advantages. Conclusion: This technique enhances clarity for safe manipulation of the round window area, improving cochlear implantation outcomes by optimizing surgical precision and reducing complications.