Background: A significant relationship between hearing loss and cognitive impairment has been previously reported. Overall, improvement in speech perception in quiet and quality of life has been observed after cochlear implantation. However, the impact of hearing loss treatment using cochlear implantation on cognitive functions is yet to be fully elucidated. Objective: To investigate the impact of cochlear implantation on cognitive and psychological functions of older adults. Study Design: Prospective patient-control study. Participants: A total of 39 participants took part in the study: 23 cochlear implant (CI) candidates (M=69.04±12.35yr) and 16 CI recipients (M=61.75±15.62yr). All participants completed an assessment of hearing (pure-tone thresholds and speech perception in quiet), and a computerised, nonverbal test battery of cognitive function assessment, as well as a depression, anxiety, and stress scale. Results: Independent-sample t test scores for the changes between 0 and 12 months revealed that CI recipients performed significantly better on measures of simple reaction time, cognitive flexibility, paired-associate learning, working memory, and strategy use (p<0.05) compared with implant candidates. Compared with the candidates, recipients also showed significantly lower stress scores (p<0.05) after 1 year use of a CI. Conclusion: Our results indicate that even in participants with a long duration, severe to profound hearing loss, cochlear implantation has some impact on improving a number of cognitive functions. This finding warrants future longitudinal investigations with a large sample size to examine if the observed cognitive enhancement benefits are sustainable.