Microglia are innate immune cells in the brain and play an essential role in the maintenance of brain immune homeostasis while their chronic overactivation is involved in the onset and exacerbation of various neurodegenerative diseases. Therefore, regulation of microglial activation is one of the therapeutic strategies for these diseases. The molecular targets for suppression of the microglial activation may include an amino acid sensor, the mammalian target of rapamycin complex 1 (mTORC1) signaling. In the present study, we hypothesized that inhibition of amino acid transporter LAT1/SLC7A5 may suppress the microglial activation by inhibiting mTORC1 signaling. Murine and human microglial cell lines BV2 and HMC3 showed a time-dependent uptake of [¹⁴C]Leu in a Na⁺ free transport buffer which was inhibited by a LAT1 inhibitor nanvuranlat. A non-competitive LAT1 inhibitor OKY-034 also suppressed the [¹⁴C]Leu uptake in a concentration-dependent manner. Thus, LAT1 is functionally expressed in the microglial cell lines and inhibited by OKY-034. Lipopolysaccharide (LPS)-induced increase in gene expressions of the proinflammatory microglial marker CD86 and the proinflammatory cytokine IL-1β was significantly suppressed by OKY-034 to a level similar to that of rapamycin, an inhibitor of mTORC1 signaling, suggesting that this LAT1 inhibitor may suppress microglial inflammation possibly by inhibiting mTORC1 signaling. Thus, LAT1 inhibitors would be possible candidates for the treatment of neurodegenerative diseases accompanied by microglial activation.