Background Air purifiers can enhance indoor air quality and health outcomes, and studies have primarily focused on high-efficiency particulate air filters and particulate matter (PM) in households. Photocatalytic oxidation (PCO) is a promising technique for eliminating gaseous pollutants and bioaerosols. However, field studies have yet to be conducted on the removal efficiency of PCO in residential settings. Therefore, this study evaluated the effects of the PCO and PCO + filters intervention on indoor air pollutants and cardiopulmonary endpoints. Methods A randomized, double-blind crossover clinical trial was conducted among 65 patients with asthma residing in a heavily industrialized urban area. Indoor air pollutants, including PM, bioaerosols, and gaseous pollutants, were measured using real-time monitoring equipment for a 24-h period. Cardiopulmonary endpoints, including lung function parameters, fractional exhaled nitric oxide, respiratory symptoms, and blood pressure were assessed before and after the intervention. Findings This was the first study to evaluate the effects of PCO and PCO + filters interventions on the levels of indoor PM, bioaerosols, and gaseous pollutants and on cardiopulmonary health in adults with asthma living in a heavily industrialized area. The PCO + filters intervention significantly reduced the levels of indoor PM 1, PM 2.5, PM 4, PM 10, total suspended particulate matter, ultrafine particles, airborne bacteria, fungi, endotoxin, mites, total volatile organic compounds, nitrogen dioxide, sulfur dioxide, and carbon monoxide. As for cardiopulmonary health, forced vital capacity (FVC)%, and FEV1% marginally increased 7 days after the PCO + filters intervention.