Purpose Although regarded as an important treatment for lymphedema, the therapeutic effects of active exercise with compression therapy (AECT) are supported by little evidence. The purpose of this study was to determine the relative benefits of AECT with different postures for patients with lower limb lymphedema (LLL). Methods Eighteen women with LLL secondary to surgical treatment of gynecological cancer, completed (1) AECT in a seated position (seated AECT), (2) AECT in a supine position (supine AECT), and (3) compression-only therapy in a supine position (CT) in this randomized, controlled, crossover trial. AECT was performed on a bicycle ergometer while wearing elastic compression bandages. Each intervention was performed for 15 min, and the three conditions were separated by a 1-week washout period. Lower-limb volumes were evaluated using a PerometerTM sensor (Pero-system, Wuppertal, Germany), and symptom severity was assessed before and after each intervention using a visual analog scale (pain, heaviness) and palpation (pitting, stiffness). The effects of the interventions were estimated using linear mixed-effect models. Results The magnitude of limb volume decreases differed significantly among the interventions, with a greater decrease after supine AECT than after CT. Pre-intervention pitting severity and skin stiffness were significantly correlated with the magnitude of volume decrease after all interventions and after AECT in the supine position, respectively. Conclusions Supine AECT using a bicycle ergometer has marked immediate effects to decrease the fluid volume of severe LLL. Clinical trial registration UMIN clinical trial registry (UMIN-CTR; ID000020129) by CONSORT 2010, TRN R000023253, December 9, 2015