AbstractPurpose:This study was performed to investigate the association between the mid-brain serotonin transporter (SERT) availability and intelligence quotient (IQ).Methods:One hundred and thirteen healthy participants, including 52 male and 61 female subjects, were recruited. We used SPECT with [123I]ADAM images to determine the SERT availability in the mid-brain, and measured the subjects’ IQ using the WAIS-R.Results:We found a significant positive correlation between the mid-brain SERT availability and the IQ of the participants. Even when controlling for age and sex, the significant association still existed.Conclusion:This result implied that the higher the SERT binding in the mid-brain, the better the IQ in healthy participants.