This report describes a patient with left-sided pneumolabyrinth following a temporal bone fracture and demonstrates characteristic positional nystagmus observed in this condition while discussing its mechanism. A previously healthy 38-year-old man presented with left-sided hearing loss, tinnitus, and positional vertigo after blunt head trauma. Temporal bone computed tomography revealed pneumolabyrinth in the ampulla of the left lateral semicircular canal (LSCC). Pure tone audiometry showed mixed hearing loss on the left (bone, 13.8 dB; air, 42.5 dB). Video Frenzel examination revealed direction-changing positional nystagmus: persistent left-beating nystagmus in the bow position, right-beating nystagmus upon moving from bowing to leaning, and persistent left-beating nystagmus in the left head-roll position only. We propose that in pneumolabyrinth involving the LSCC, changes in head position shift the air bubble, generating a buoyant force that indents the endolymphatic membrane and deflects the cupula, producing positional nystagmus. The direction of nystagmus may vary depending on the bubble’s location.