Oral mucositis (OM) is a life-threatening side effect of chemo-radiotherapy. OM can provide a portal of entry for many microorganisms as coinfections which potentially generate other oral lesions. This case report describes a holistic approach to obtaining the successful treatment of OM with necrotizing ulcerative stomatitis (NUS) and oral candidiasis as coinfections in pediatric acute lymphoblastic leukemia (ALL). A 2-year-8-month-old boy was referred from the Pediatrics Department at Dr. Hasan Sadikin General Hospital with the chief complaint of canker sore and eating difficulty for the past two weeks. He had undergone the twelfth cycle of the last chemotherapy using methotrexate regimen. Extraoral examination revealed anemic conjunctiva, icteric sclera, and dry lips. Well-defined irregular multiple ulcers covered by yellowish to grayish pseudomembranous were found on the upper and lower labial mucosa, right and left buccal mucosa, tongue, palate, and gingiva. Potassium hydroxide (KOH) examination showed fungi in the oral lesions smear. The established diagnosis was OM with NUS and oral candidiasis as coinfections. Debridement was done using chlorine dioxide-zinc and 0.2% chlorhexidine gluconate. We collaborated with the pediatrician who prescribed ceftazidime, meropenem, and fluconazole, and also with parents. The holistic approach is beneficial and important in improving quality of life and supporting the successful treatment of OM with coinfections.