Background: There always has been a question about the best age for cochlear implantation (CI) in prelingual deaf children. The age factor in the outcome of cochlear implantation in prelingual deaf children has been the subject of many studies. The aim of the present study was to find the effect of age at the time of implantation on hearing threshold of these children. Methods: One hundred and nine prelingual deaf children who had undergone CI were enrolled. The mean hearing threshold (HT) at octave intervals from 125 to 8000 Hz at different periods from the operation time were compared between those patients whose age at the time of implantation were less than 24 months and those whose age were equal or greater than 24 months. Results: The mean age of patients at the time of implantation was 38.9 months and a half of them had less than 28 months. There was no difference in mean HT between the two age groups across different measurement periods. A multiple regression model showed that device type was the sole significant predictor of mean HT at the first and third months after implantation, where age replaced it at the sixth month. Conclusion: These results suggest that what had been found in other studies as a favorable effect of younger age at the time of implantation on speech perception cannot be explained by a better hearing, and there are other important factors including rehabilitation programs beginning at a younger age that may explain those findings.