Salvianolic acid B (SalB) a water‑soluble phenolic compound, extracted from Salvia miltiorrhiza, has previously been demonstrated to reverse tumor multidrug resistance (MDR), including in colorectal cancer. Reactive oxygen species (ROS) are oxygen radicals generated during aerobic metabolism (superoxide and hydroxyl radicals) and superoxide easily generating free radicals (H2O2). The concept that increased ROS levels can lead to augmented tumor cell‑sensitivity to chemotherapy drugs has become notable. The aim of the present study was to elucidate the role of ROS in mediating the effect of SalB on drug resistance and the correlation with drug resistance‑associated protein, P‑glycoprotein (P‑gp), and apoptosis‑associated proteins, B‑cell lymphoma 2 (Bcl‑2) and Bcl‑2‑associated X (Bax). In the current study, through utilizing the multidrug resistant colorectal cancer cell line, HCT‑8/VCR, it was demonstrate that SalB reversed MDR in HCT‑8/VCR. In addition, SalB significantly increased ROS levels, which may have accelerated the apoptosis of HCT‑8/VCR cells by downregulating Bcl‑2 and increasing Bax protein expression. Furthermore the increased intracellular ROS levels may have inhibited P‑gp expression at the gene and protein levels. In conclusion, the data of the current study demonstrate that SalB reversed MDR in HCT‑8/VCR cells, and the effect is associated with increased ROS levels, which may downregulate P‑gp expression and promote tumor cell apoptosis, which in turn increases the sensitivity of drug‑resistant cells to chemotherapy drugs.