OBJECTIVE : The existing yet limited prospective studies reported conflicting results about obesity and hearing loss. We investigated the prospective association between obesity and hearing loss in a large-scale Japanese working population, as well as the association between metabolic phenotype and hearing loss. METHODS : The study included 48,549 employees aged 20-64 years and free of hearing loss at baseline. Pure-tone audiometric testing was performed annually to identify hearing loss at 1 and 4 kHz. Cox proportional hazards regression was used to investigate the risk of hearing loss associated with body mass index (BMI) and metabolic phenotype (based on a BMI of ≥25.0/<25.0 kg/m2 and presence/absence of ≥2 components of metabolic syndrome, except waist circumference). Baseline and updated information were obtained from annual health checkups. RESULTS : With a median follow-up of 7 years, 1595 and 3625 individuals developed unilateral hearing loss at 1 and 4 kHz, respectively. The adjusted hazard ratios (HR) for hearing loss at 1 kHz were 1.21 (1.08, 1.36) and 1.66 (1.33, 2.08) for those with BMI 25.0-29.9 kg/m2 and BMI ≥30.0 kg/m2, respectively, compared to individuals with BMI <25.0 kg/m2. For hearing loss at 4 kHz, the corresponding HRs were 1.14 (1.05, 1.23) and 1.29 (1.09, 1.52). Compared with metabolically healthy non-obese individuals, the adjusted HRs for hearing loss at 1 kHz were 1.19 (1.03, 1.39), 1.27 (1.01, 1.61), and 1.48 (1.25, 1.76) for unhealthy non-obese, healthy obese, and unhealthy obese individuals, respectively. For hearing loss at 4 kHz, the corresponding HRs were 1.13 (1.04, 1.25), 1.21 (1.04, 1.41), and 1.26 (1.12, 1.41). CONCLUSIONS : Overweight and obesity are associated with an increased risk of hearing loss, and metabolically unhealthy obesity may confer additional risk.