The decline of physical function during chemotherapy predicts poor quality of life and premature death. It is unknown if resistance training prevents physical function decline during chemotherapy in colon cancer survivors. This multicenter trial randomly assigned 181 colon cancer survivors receiving postoperative chemotherapy to home-based resistance training or usual care control. Physical function outcomes included the short physical performance battery, isometric handgrip strength, and the physical function subscale of the Medical Outcomes Short-Form 36-item questionnaire. Mixed models for repeated measures quantified estimated treatment differences. At baseline, participants had a mean (SD) age of 55.2 (12.8) years; 67 (37%) were 60 years or older, and 29 (16%) had a composite short physical performance battery score of no more than 9. Compared with usual care control, resistance training did not improve the composite short physical performance battery score (estimated treatment difference = -0.01, 95% confidence interval [CI] = -0.32 to 0.31; P = .98) or the short physical performance battery scores for balance (estimated treatment difference = 0.01, 95% CI = -0.10 to 0.11; P = .93), gait speed (estimated treatment difference = 0.08, 95% CI = -0.06 to 0.22; P = .28), and sit-to-stand (estimated treatment difference = -0.08, 95% CI = -0.29 to 0.13; P = .46). Compared with usual care control, resistance training did not improve isometric handgrip strength (estimated treatment difference = 1.50 kg, 95% CI = -1.06 to 4.05; P = .25) or self-reported physical function (estimated treatment difference = -3.55, 95% CI = -10.03 to 2.94); P = .28). The baseline short physical performance battery balance score (r = 0.21, 95% CI = 0.07 to 0.35) and handgrip strength (r = 0.23, 95% CI = 0.09 to 0.36) correlated with chemotherapy relative dose intensity. Among colon cancer survivors with relatively high physical functioning, random assignment to home-based resistance training did not prevent physical function decline during chemotherapy. NCT03291951.