Rationale: Patients with anterior cruciate ligament (ACL) reconstruction often have poor adherence to post-surgery rehabilitation. Objective: This study applied the integrated model of self-determination theory and the theory of planned behavior to examine the effects of a smartphone-delivered intervention on the recovery outcomes of patients with an ACL rupture during post-surgery rehabilitation period. Additionally, we explored the effects of the intervention on participants with different beliefs toward rehabilitation at baseline. Methods: The randomized control trial recruited 96 eligible participants (M age = 27.82 years, SD = 8.73; female = 39%) who underwent ACL reconstruction surgery. Participants were randomly assigned to an intervention group (n = 41), which received standard post-surgical treatment (usual-care) and smartphone application (“ACL-Well”), or a usual-care control group (n = 55). The primary outcomes were recovery outcomes from ACL surgery measured by knee muscle strength and laxity, and subjective knee evaluation completed 4-month post-intervention. Secondary outcomes were the psychological and behavioral outcomes measured at baseline, at 2- and 4-month post-intervention. Results: ANCOVA indicated no significant between-group differences in primary outcomes: knee muscle strength, knee laxity and subjective knee evaluation, Fs(1, 27 to 55) = 0.01 to 1.36, p =.25 to.99, η2 = 0.01 to 0.03. For the secondary outcomes, growth mixture modelling revealed self-determined treatment motivation declined significantly over the intervention period in the control group (M slope = −0.39 to −0.12, p =.01 to.04), but not in the intervention group (M slope = −0.19 to −0.08, p =.06 to.38). Conclusions: The smartphone application fell short in promoting orthopedic outpatients' recovery outcomes. Yet, it shows some promises as a mean to maintain patients’ motivation and adherence to treatment.