We are interested in investigating whether cancer therapy may alter the mitochondrial redox state in cancer cells to inhibit their growth and survival. The redox state can be imaged by the redox scanner that collects the fluorescence signals from both the oxidized-flavoproteins (Fp) and the reduced form of nicotinamide adenine dinucleotide (NADH) in snap-frozen tissues and has been previously employed to study tumor aggressiveness and treatment responses. Here, with the redox scanner we investigated the effects of chemotherapy on mouse xenografts of a human diffuse large B-cell lymphoma cell line (DLCL2). The mice were treated with CHOP therapy, i.e., cyclophosphamide (C)＋ hydroxydoxorubicin (H) Oncovin (O) prednisone (P) with CHO administration on day 1 and prednisone administration on days 1-5. The Fp content of the treated group was significantly decreased (p = 0:033) on day 5, and the mitochondrial redox state of the treated group was slightly more reduced than that of the control group (p = 0:048). The decrease of the Fp heterogeneity (measured by the mean standard deviation) had a border-line statistical significance (p = 0:071). The result suggests that the mitochondrial metabolism of lymphoma cells was slightly suppressed and the lymphomas became less aggressive after the CHOP therapy.