Abstract: Provided are a novel process for preparing (3R,4R)-1-benzyl-N,4-dimethylpiperidin-3-amine or a salt thereof, which is an intermediate useful for the preparation of tofacitinib, an intermediate used in the process, i.e., isopropanol solvate of methyl ((3R,4R)-1-benzyl-4-methylpiperidin-3-yl)carbamate dibenzoyl-L-tartrate, an intermediate, having excellent stability, useful for the preparation of tofacitinib, i.e., (3R,4R)-1-benzyl-N,4-dimethylpiperidin-3-amine acetate, and a process for preparing tofacitinib or a pharmaceutically acceptable salt thereof.