ObjiectiveTo explore the efficacy and safety of ketogenic diet therapy (KDT) in the rapidly progressive stage of childhood developmental epileptic encephalopathy Dravet syndrome (DS). Methods The clinical data of all patients who added KDT in the Children’s Hospital of Fudan University from 2011 to 2022 were retrospectively collected, and the age of <6 years was used as the criterion for the rapid progression of the disease. The clinica data, genotype and the efficacy of KDT were analyzed in DS patients who met the criteria. Results A total of 32 patients met the criteria for rapid disease progress, including 22 males and 10 females. The age at onset was (5.69±2.10) months. All patients had multiple seizure phenotypes and monthly seizures despite reasonable Antiseizure medications treatment. After 3, 6, 12, and ≥24 months, 93.8% (30/32), 87.5% (28/32), 53.1% (17/32), 34.4% (11/32) remained on the KDT, while 76.7% (23/30), 75.0% (21/28), 70.6% (12/17), 54.5% (6/11) showed >50% reduction in seizure. Status epileptius (SE) was reduced by 100% at 3 months, 71.0% at 6 months, 86.0% at 12 months. After 12 months, 14 patients experienced efficacy degradation. After 3 months, the EEG background rhythm showed improvement in 75.0% patients, interictal epileptic discharges was decreased in 54.5% patients and cognitive function was improved in 78.6% patients. At the initial stage of KDT, 62.5% (20/32) patients had transisent adverse reactions, including diarrhea, vomiting, fatigue, lethargy, hypoglycemia, and metabolic acidosis, but no mid- and long-term adverse reactions were found. ConclusionKDT is an efficective and safe treatment for DS. KDT can effectively control seizures, reduce the incidence of Status SE and shorten the duration of SE. With the prolongation of the KDT course, some patients experienced a degraded effect. KDT can improve abnormal EEG and cognitive function in DS patients. Pharmoco-resistant DS patients are suggested to receive KDT in the early stage of disease progression.