ObjectiveTo investigate the clinical electrophysiological characteristics of Cyclin-dependent kinase-like 5 gene induced developmental epileptic encephalopathy (CDKL5-DEE). MethodsThe clinical data and series of video EEGs of children with CDKL5-associated developmental epileptic encephalopathy (CDKL5-DEE) who were admitted to the Children’s Medical Center of Peking University First Hospital from June 2016 to May 2024 were retrospectively analyzed. Results A total of 16 patients with CDKL5-DEE were enrolled, including 13 females and 3 males. All patients had de novo variants of CDKL5 gene, including 6 cases of missense variants, 5 cases of frameshift variants, 4 cases of nonsense variants, and 1 case of large fragment deletion. The age of onset was 8 days (d) after birth ~1 year (y) and 10 months (m), and the median age was (85.94±95.76) days. Types of seizures at onset: 4 cases of tonic seizures [age of onset 10~52 days, median age (25.5±15.84) days]; There were 5 cases of focal seizures [age of onset 8 d~8 m, median age (77.76±85.97) d]. There were 4 cases of epileptic spasmodic seizures [age of onset 3 m~1 y 10 m, median age (6.25±3.49) m]; There were 2 cases of bilateral tonic-clonic seizures [age of onset 30~40 days, median age (35.00±5.00) days]; focal concurrent epileptic spasm seizures 1 case (age of onset 2 m). A total of 59 VEEG sessions were performed in the pediatric EEG room of Peking University First Hospital for 4 hours. All the results were abnormal, including 26 normal background, 25 slow rhythm difference with background, and 8 no background. The interictal was 16 posterior or focal discharges, 19 multifocal discharges, 17 generalized or accompanied by focal/multifocal discharges, and 7 hypsarrhythmia; The ictal was 33 epileptic seizures, 6 myoclonic seizures, 5 focal seizures, 2 tonic-clonic seizures, 2 atypical absence seizures, 2 tonic seizures, 1 myoclonic sequential focal seizure, 1 focal sequential epileptic spasm, and 1 hypermotor-tonic-spasms. The background of patients within 6 months of age was normal, and the background abnormality increased significantly with age. generalized discharges are evident after 2 years of age between seizures. Conclusion CDKL5-DEE seizures have an early onset and are refractory to medications. Epileptic spasms are the most common type of seizure in every patient and long-lasting, with generalized seizures increasing markedly with age. EEG is characterized by a normal background within 6 months. With the increase of age, the background and interictal discharges have a tendency to deteriorate.