The therapeutic potential of monoacylglycerol lipase (MAGL) inhibitors in central nervous system-related diseases has attracted attention worldwide. However, the availability of reversible-type inhibitor is still limited to clarify the pharmacological effect. Herein, we report the discovery of novel spiro chemical series as potent and reversible MAGL inhibitors with a different binding mode to MAGL using Arg57 and His121. Starting from hit compound 1 and its co-crystal structure with MAGL, structure-based drug discovery (SBDD) approach enabled us to generate various spiro scaffolds like 2a (azetidine-lactam), 2b (cyclobutane-lactam), and 2d (cyclobutane-carbamate) as novel bioisosteres of 3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-6-yl moiety in 1 with higher lipophilic ligand efficiency (LLE). Optimization of the left hand side afforded 4f as a promising reversible MAGL inhibitor, which showed potent in vitro MAGL inhibitory activity (IC50 6.2 nM), good oral absorption, blood-brain barrier penetration, and significant pharmacodynamic changes (2-arachidonoylglycerol increase and arachidonic acid decrease) at 0.3-10 mg/kg, po. in mice.