Purpose: The main purpose of the current study was to assess the development of auditory and speech perception and the effects of the age at implantation in CI children after long-period follow up. Materials and methods: Five hundred and forty-four young children participated in this study (339 males and 205 females). The age at implantation ranged from 6 months to 36 months. All subjects were prelingually bilateral profound sensorineural hearing loss. They were divided into 3 groups according to the implant ages: group 1 (age at implantation < 12 months, n = 109); group 2 (12 months < age at implantation < 24 months, n = 284); and group 3 (24 months < age at implantation < 36 months, n = 151). The categorical auditory performance (CAP) was used to assess auditory abilities and the speech intelligibility rating (SIR) was used to assess the speech intelligibility of these CI children. The tests were administered at pre-surgery and 1, 3, 6, 12, 24, 36, 48- and 60-months post-surgery. Results: All the subjects demonstrated improvements of auditory abilities and speech intelligibility after CI surgery. The auditory ability developed quickly in 12 months after implantation. However, the speech intelligibility scores show rapid improvement within 24 months post implantation. Significant difference was found between group 1 and group 3, group 2 and group 3 before 12 months post-implantation for CAP and SIR. The three groups of children showed similar development pattern for their auditory abilities and speech intelligibility. Conclusion: The results of this study suggested dramatic and continuous improvement of the auditory and speech abilities post implantation in these CI children. Furthermore, the age at implantation played a considerably smaller role in the improvement of hearing and speech abilities. However, earlier implantation still benefits the language development.