BackgroundRadiotherapy is used to treat oral cancer, yet it negatively affects patients' health‐related quality of life (HRQOL). The aim was to evaluate the impact of an oral healthcare intervention on HRQOL of patients with oral cancer who receive radiotherapy with or without chemotherapy.MethodsAn oral healthcare intervention was provided to 41 patients with oral cancer before radiotherapy (fluoride varnish application, scaling, permanent restorations, adjustment of sharp teeth, and extraction of teeth with questionable prognosis, oral hygiene instructions), during, and 3 months after radiotherapy (baking soda mouthwash, artificial saliva spray). EORTC QLQ‐H&N35 was used to compare the HRQOL of the intervention and control groups, with the latter having received routine oral healthcare.ResultsThe intervention group showed lesser values for HRQOL domains and items indicating fewer side effects during the last week of radiotherapy and 3 months after, compared to the control group. Most of the changes in HRQOL were significantly less in the intervention group compared to the control group (p < 0.01).ConclusionThe oral healthcare intervention effectively reduced the effect of radiotherapy and positively impacted on HRQOL of patients with oral cancer.