This article reviews the cognitive processes and neural mechanisms of second language acquisition of Chinese English learners. The first issue addressed is whether there is a critical period in second language learning Behavioral and brain imaging research do not provide sufficient evidence for this hypothesis. Though there is correlation found between age of acquisition and second language learning, albeit it was in the situation of ESL (English as Second Language). Given that age of acquisition does influence language acquisition, the effect was limited to phonology, while its effect on syntax scarce, and vocabulary not at all English learning in Taiwan is EFL (English as Foreign Language) instead of ESL. Whether the conclusion drawn from ESL can be adequately applied upon EFL needs to be further discussed by examining whether there is a parallel pattern of cognitive processing mechanism and language environment between ESL and EFL. This research also shows that speakers whose mother-tongue is Chinese at least do have some inhibitions with phonology when learning English as a foreign language.