Schisandrin B (Sch.B) shows antineoplastic activity in colorectal cancer, but the mechanism is still obscure. The intracellular spatial distribution may be helpful in elucidating the mechanism. To investigate the intracellular drug distribution of Sch.B in cancer cells, a simple, rapid, and sensitive ultra-highperformance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was established for the determination of Sch.B in colorectal cancer cells. Warfarin was utilized as an internal standard. The sample pretreatment was carried out with protein precipitation using methanol. The analyte was separated on an Atlantis T3-C18column (3μm, 2.1∗100 mm) using gradient elution with a mobile phase comprised of methanol and 0.2% formic acid in water. The flow rate was 0.4 mL/min. The linear range of Sch.B was 20.0–1000.0 ng/mL with a correlation coefficient (R) more than 0.99. The matrix effect and recovery ranged from 88.01% to 94.59% and from 85.25% to 91.71%; the interday and intraday precision and accuracy, stability, specificity, carryover, matrix effect, and recovery all conformed to the requirements of pharmacopoeia. Cell viability and apoptosis assays demonstrated that Sch.B has an inhibitory effect in a dose-dependent way on HCT116 proliferation and achieved significant suppression at 75μM (IC50). It was found that in HCT116 cell, nucleus, and mitochondria, exposure levels of Sch.B peaked at 36 h and then decreased, and mitochondria possessed more Sch.B than nucleus. These results may help to elucidate the antitumor effect of Sch.B.