Oral capecitabine improves convenience compared to intravenous therapies but presents monitoring challenges. We conducted a randomized pilot trial to evaluate a mobile health intervention to remotely monitor capecitabine adherence and patient-reported outcomes (PROs) among women with breast cancer. Patients with breast cancer prescribed capecitabine, an oral chemotherapy with a complex, cyclical regimen, were randomly assigned to enhanced usual care (EUC) or PRO arm. Participants were asked to use a smart pill bottle to measure adherence (timing and dose) and complete baseline and 90-day follow-up surveys. PRO participants received text messages for missed or incorrect doses and weekly text-based symptom assessments, and their oncologists received alerts for severe symptoms or missed doses. We compared nonadherence (<80%) and changes from enrollment to follow-up on reported physical and mental health quality-of-life scores and number of severe symptoms by study arm. Overall, 32 women were randomly assigned (17 EUC and 15 PRO): 28 (87.5%) received the intervention and 24 (78.1%) completed the follow-up survey. Among participants who received the intervention, PRO participants responded to 83.3% of symptom questions; 7.7% of PRO participants were nonadherent compared with 40.0% of EUC participants (P = .049). Among those who completed the follow-up survey, 12.5% of PRO participants had reductions in their mental health composite scores compared with 69.2% of EUC participants (P = .011); 10% of PRO participants had more severe symptoms at follow-up compared with 57.1% of EUC participants (P = .019). A mobile health intervention using text message reminders and symptom assessments improved medication adherence and mental health quality-of-life scores and lowered symptom burden of patients with breast cancer prescribed capecitabine. Future work should evaluate the longer-term impacts of this intervention.