Objective: To investigate a new style of resistance exercise using elastic bands and explore its therapeutic effect on the lower-extremity function of female patients with osteoarthritis (OA) of the knee. Design: A randomized, controlled clinical trial. Setting: University-affiliated medical center. Participants: Forty-one women with mild-to-moderate knee OA were randomly assigned to one of two groups, an exercise group (n = 24; age: 65.0 ± 8.4 years), and a control group (n = 17; age: 70.8 ± 8.4 years). Interventions: The exercise group performed supervised exercise with elastic bands in addition to conventional modality treatments two to three times a week for 8 weeks. The control group received only the conventional modality treatments over the same period. Main outcome measures: The distance of the functional forward-reach, 30 s chair stand repetitions, walking function (time of a 10 m walk, timed up-and-go, and going up-and-down 13-stair tests), and Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index scores. Results: Statistically significant improvements in all measures were observed in the exercise group after 8 weeks (p < 0.001). Except for the outcomes on the functional forward-reach (p = 0.108) and going up-and-down 13-stair test (p = 0.278), there were significant differences in the extent of improvement between the two groups. Positive changes in the 30 s chair stand test, 10 m walk test, and timed up-and-go test were 2.5 ± 1.4 repetitions, 1.4 ± 1.2 s, and 1.6 ± 1.1 s in the exercise group, which were significant better than those in the control group (0.6 ± 0.9 repetitions, 0.5 ± 1.1 s, and 0.3 ± 1.1 s, respectively) (p ≤ 0.001). The lower scores of all three subscales of the WOMAC index were significant after 8 weeks (p ≤ 0.05), especially for pain (−2.3 ± 1.3) and physical function (−10.7 ± 5.9) (both p ≤ 0.01), and the improvements were all significant better than those of the control group (p ≤ 0.05). Conclusions: A new style of resistance exercise using elastic bands with four color combinations (yellow-red, red-red, red-green, and green-green) over a period of 8 weeks can significantly improve lower-extremity function among females with mild-to-moderate knee OA.Implications for RehabilitationResistance exercise is an effective means of improving the lower extremity function for people with knee osteoarthritis (OA).A new model for using elastic bands combinations based on leg-press exercise and the principles of progressive resistance training leads to improved lower extremity function in female patients with knee OA after an 8-week period.