Absolute pitch (AP) is the ability to label the pitch of tones without any reference tones. Previous studies have shown that the anatomical and functional basis of AP exists in the superior temporal gyrus (STG), although the associated neurotransmitters remain unknown. We used proton magnetic resonance spectroscopy to quantify the concentration of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, in the bilateral STG of adult AP possessor and non-AP possessors. We found a significant negative correlation between AP scores and GABA concentration in the left STG. Furthermore, mean GABA concentration was significantly reduced in the AP possessors group compared to the non-AP possessors group. Our results suggest that less inhibition in the bilateral STG may enable AP possessors to associate categorical labels with tones.