Abstract Background Although recent advances in knee osteoarthritis (OA) treatment and evaluation were achieved, to the best of our knowledge, few studies have evaluated the longitudinal effect of therapeutic modalities on the functional exercise capacity of patients with knee OA. The purpose was to investigate the effects of kinesiotherapy and electrotherapy on functional exercise capacity, evaluated using the six-minute walk test (6-MWT) in patients with bilateral knee OA. Secondary measurements included range of motion (ROM), severity of knee pain (VAS), and a measure of perceived health and physical function, evaluated using the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index. Methods A total of 40 women with bilateral knee OA were assigned to three groups: kinesiotherapy (KIN, n = 16), transcutaneous electrical nerve stimulation (TENS, n = 12), or ultrasound (US, n = 10). The groups underwent 12 weeks of intervention twice per week. The participants were subjected to the 6-MWT, ROM, VAS and WOMAC index. These tests were performed before and after the intervention. The study was focused on outpatients and was carried out at Universidade Estadual de Campinas, Brazil. Results At follow-up, the KIN and US groups had significantly higher 6-MWT distances (19.8 ± 21.7 and 14.1 ± 22.5%, respectively) compared with their respective pre-intervention values. All treatments were effective for reducing pain and improving the WOMAC index. Conclusions We demonstrated that the 6-MWT is a tool that can be used to evaluate improvements in the functional exercise capacity of patients submitted to a clinical intervention.