Chemosensory (gustatory and olfactory) dysfunction contributes to obesity, but the association between body mass index (BMI) and chemosensory dysfunction are inconsistently reported. The present study included 4,390 subjects at a Smell and Taste Clinic. Results suggested that both the obesity class II group (BMI ≥ 35) and underweight group (BMI < 18.5) exhibited impaired taste function compared with the normal weight group (p <.05). Comparing with the other groups, the obesity class II group exhibited a higher proportion of impaired bitter identification (8.6%), and the underweight group showed a higher proportion of impaired salty identification (7.9%). When investigating differences for individual tastes, subjects with impaired bitter identification had higher BMI (t = 2.79, p =.005) and lower olfactory scores (p <.05) compared with those with intact bitter identification. Finally, reduced taste scores are associated with an increased BMI (r = −.04, p =.022). This correlation becomes more pronounced with age (F = 1.42, p <.001). Practical Application: The nonlinear association between chemosensory dysfunction and BMI suggested that maintaining the gustatory and olfactory function is of significance for normal metabolism. In obesity regulating bitter taste appears to be more important than the other tastes.