Daily life requires many decisions. People with high metacognition may effectively and quickly make decisions. We used functional magnetic resonance imaging (fMRI) to examine the neural basis of the relationship between metacognition and self-related decision-making. Tokyo Metropolitan University Research Ethics Committee (No. 14072) approved this study. Participants included 13 young, healthy, right-handed people (mean age ± standard deviation: 21.38 ± 1.12 years, range 20–24 years). Before fMRI scanning, explicit self-esteem and metacognition were assessed using the Rosenberg Self-esteem Scale (RSES) and Metacognitive Awareness Inventory (MAI), respectively. Using a computer mouse, subjects answered decision-making task questions, which were randomly presented during scanning. Condition 1 (self-related decision-making) asked, “If given these 2 types of work, which would you do first?” Condition 2 (word decision-making) asked, “Which of the 2 words is longer?” The 2 presented words were randomized and the same for each condition. We analyzed differences between these conditions using SPM12 implemented in MATLAB R2017a. We also analyzed the correlation between the MAI scores (Factor 1: monitoring; Factor 2: control; Factor 3: metacognitive knowledge) and RSES scores and the averaged parameter estimates in the spherical region of interest. The left orbitofrontal cortex, left superior frontal gyrus, left inferior frontal gyrus, left angular gyrus, left temporal pole, bilateral middle temporal gyrus (MTG), and left hippocampus were activated in self-related compared with word decision-making. MAI Factor 1 and 3 scores were negatively correlated with the MTG ( r = −0.84 and r = −0.71, respectively; P < 0.05). MAI Factor 2 was not significantly correlated with any activity. The negative correlation between MAI Factor 1 and 3 scores and MTG activity disagrees with previous reports that MTG is involved in higher subjective confidence ratings. Moreover, metacognitive control may be regulated by other brain areas.