Abstract Introduction The apolipoprotein B/apolipoprotein A1 (ApoB/ApoA1) ratio is recognized as a clinical indicator of cardiovascular disease and ischemic cerebral disease. Cerebrovascular dysfunction is also involved in head and neck radiotherapy. The aim of this study was to investigate the correlation between ApoB/ApoA1 ratio and the severity of radiation‐induced brain necrosis (RN) in patients who underwent radiotherapy after nasopharyngeal carcinoma (NPC). Methods In this retrospective study, 191 NPC patients diagnosed with RN were evaluated. Clinical characteristics, serum lipid, apolipoproteins, and brain magnetic resonance imaging findings were collected. Serum lipid and apolipoproteins were quantified using standard diagnostic assays, and the quality of life (QOL) was assessed by the World Health Organization quality of life abbreviated instrument (WHOQOL‐BREF). Results ApoB/ApoA1 ratio was positively correlated with lesion volume (r = .18, p = .03) and negatively correlated with WHOQOL‐BREF scores (r = −.28, p