Cochlear implantation (CI) is an effective therapy for patients with severe to profound sensorineural hearing loss. It remains controversial whether children younger than 12 months of age should undergo CI. To evaluate the safety and effectiveness of CI in children younger than 12 months of age. We performed a retrospective study of clinical data of pediatric patients younger than 12 months of age who underwent CI and were followed up for 1 to 2 years. Patients' developmental levels were evaluated by the Gesell score before CI. Intraoperative and postoperative complications were recorded to evaluate the safety of CI. Auditory and speech abilities were scored by the LittlEARS® auditory questionnaire (LEAQ), categories of auditory performance (CAP), speech intelligibility rating (SIR), infant-toddler meaningful auditory integration scale (IT-MAIS), and meaningful use of speech scale (MUSS) at 1, 2, 3, 6, 9, and 12 months after CI. The associations between clinical characteristics before CI and postoperative scores at 1 year after CI were analyzed by the linear mixed-effects model. Eighty-nine children (47 boys and 42 girls) were included in this study (mean age at CI, 9.2 ± 1.6 months). Sixteen patients were diagnosed with cochlear malformation and 16 underwent bilateral CI. No severe complications occurred in any patients. The mean developmental quotient of the Gesell score was 78.00 ± 10.03. The median LEAQ scores were 0, 5, 10, 16, 22, 26 and 30 before and at 1, 2, 3, 6, 9, and 12 months after CI, respectively. These findings implied that the LEAQ score greatly improved in the first year after CI. The overall CAP, SIR, IT-MAIS, and MUSS scores also increased with increasing duration after CI. No significant associations were detected between clinical characteristics (age, sex, implant number, pre-CI Gesell score, and inner ear malformation) and LEAQ outcomes at 12 months after CI. With increasing duration after CI, auditory and speech behavior dramatically improve in young children. Our findings indicate that CI is feasible for children younger than 12 months of age. © 2020 Chinese Medical Association. Pediatric Investigation published by John Wiley & Sons Australia, Ltd on behalf of Futang Research Center of Pediatric Development.