Recent studies have reported speech intelligibility in noisy environment from cochlear implant (CI) users was reduced because the spectral resolution is not high enough. For the user who had only implanted one CI in unilateral ear, combined a hearing aid (HA) in contralateral ear, known as bimodal hearing, can improved the speech perception. This is partly true due to the residual low frequency acoustic information provided from HA can help CI users to segregate the target speech from noise. In this study, a vocoder was conducted to evaluate the effect of low frequency information, especially the fundamental frequency (F0), in recognizing Taiwanese Mandarin for bimodal CI users. The result showed that F0 was the main factor in low frequency acoustic information, and bimodal apparently enhance the performance of speech recognition in noise in Taiwanese Mandarin.