OBJECTIVE: To screen 6′-hydroxy justicidin A(JR6)-sensitive tumor cells and explore the cell redox function. METHODS: The human bladder cancer cells EJ, human liver cancer cells Bel, human lung cancer cells A549, human colon cancer cells HCT-8 and HT-29, human gastric cancer cells BGC, human colorectal cancer cells LS180, human cervical cancer cells HeLa, human hepatoma cells HepG2, and human breast cancer cells MCF-7 were divided into normal control group, positive control cisplatin, doxorubicin, teniposide, etoposide, 5-fluorouracil groups and JR6 group. The effect of JR6 and positive drugs on inhibition in 10 tumor cell lines for 48 h was measured using MTT method and the values of IC50 were calculated by the methods of curvilinear regression. After EJ cells were cultured with JR6 3.02, 9.07, 27.2, 81.7 and 245 μmol·L-1 for 48 h, the activities of superoxide dismutase (SOD), glutathion peroxidase (GSH-Px), and catalase (CAT) as wall as the content of malondialdehyde (MDA) in EJ cells were detected. EJ cells were divided into exogenous SOD +doxorubicin 9.19 μmol·L-1 and exogenous SOD + JR6 3.02, 9.07, 27.2, 81.7 and 245 μmol·L-1 groups. Proliferation of sensitive cells was measured by MTT method. After EJ cells were cultured with doxorubicin 9.19 μmol·L-1 and JR6 12.3 , 49.0 and 196 μmol·L-1 for 24 h, the generation of reactive oxygen species in JR6-sensitive tumor cells was measured by laser scanning confocal microscopy. RESULTS: MTT assay results showed EJ cells were sensitive to JR6, and IC50 of JR6 in EJ cells was 57.1 μmol·L -1, while IC50 of JR6 in other tumor cells ranged from 71.3 to 124 μmol·L-1. Compared with normal control group, doxorubicin 9.19 μmol·L-1 decreased activities of SOD by (64.3 ± 2.1)%, GSH-Px by (66.5 ± 3.5)% and CAT by (49.6 ± 1.9)%, but increased the content of MDA by (432 ± 5.4)% in EJ cells (P < 0.01). JR6 3.02, 9.07, 27.2, 81.7 and 245 μmol·L-1 significantly decreased activities of SOD (7.28 ± 0.3)%, (57.1 ± 3.2)%, (66.5 ± 4.7)%, (72.1 ± 5.5)% and (78.7 ± 2.4)%, decreased GSH-Px (20.3 ± 1.6)%, (32.8 ± 2.3)%, (45.3 ± 3.6)%, (59.3 ± 4.5)% and (71.9 ± 4.2)%, decreased CAT (10.1 ± 0.6)%, (15.9 ± 0.7)%, (25.9 ± 2.3)%, (38.8 ± 3.5)%, (52.4 ± 3.9)% in EJ cells, respectively; and JR6 3.02, 9.07, 27.2, 81.7 and 245 μmol·L-1 raised the content of MDA (24.4 ± 1.3)%, (90.2 ± 8.7)%, (217.0 ± 19.0)%, (356.0 ± 24.0)% and (539.0 ± 32.0)%, respctively. Exogenous SOD could protect against the inhibition effect of doxorubicin 9.19 μmol·L-1 and JR6 3.02, 9.07, 27.2, 81.7 and 245 μmol·L-1 on EJ cells, compared with no exogenous SOD group (P < 0.05). Compared with normal control group, doxorubicin 9.19 μmol·L-1 increased content of reactive oxygen species by (43.0 ± 2.1)%, JR6 12.3, 49.0 and 196 μmol·L-1 increased contents of reactive oxygen species by (40.7 ± 0.7)%, (84.1 ± 6.3)% and (151.0 ± 2.9)%, respectively. CONCLUSION: The human bladder cancer cell line EJ is JR6-sensitive. JR6 interferes the intracellular balance of redox system to inhibit proliferation of EJ cells. Exogenous SOD can protect against the inhibition effect of JR6 in EJ cells.