Children with developmental and behavioral problems including autistic spectrum disorders (ASDs) may have inappropriate feeding behaviors, which leads to an increased risk of multiple nutrient deficiencies. Vitamin C deficiency is one of the common nutrient deficiencies reported in children with inappropriate feeding. This case report illustrates two cases of ASD children with a clinical presentation of pulmonary arterial hypertension, a rare presentation of vitamin C deficiency. Vitamin C supplementation, pulmonary vasodilator, and supportive treatment were provided. Patients could recover from the illness and could be discharged from the hospital in a short time. In addition to vitamin C, the patients also had multiple micronutrient deficiencies. Nutrition counseling was given and micronutrient supplement was continued until follow-up. Regular nutrition assessment and counseling among children with ASD are needed to prevent nutrient deficiencies which may lead to life-threatening complications.