Learning vocabulary in any foreign language including English is vital, since it plays a central role in language learning. However, when compared to other skills, it is undoubtedly the most time-consuming skill to be mastered by learners and users of English due to various reasons. While learners exert much effort to memorise, store, and retrieve words and word groups either in isolation or in chunks, they face a wide range of problems that exacerbate vocabulary learning. This paper primarily aims to discuss one particular group of difficulties of learners/users experience while learning English vocabulary through the lenses of psycholinguistics, in which speaking of vocabulary, attention falls to learners' use of mental process while memorising, storing, using and understanding words and word groups in English. To this end, the paper looks for answers to the questions, such as whether some vocabulary items--words are easier to learn and others not, what it means to know a word, what makes a word difficult to be stored and retrieved by learners/users, and what psychological and linguistic factors affect effective vocabulary learning. While doing so, the field of psycholinguistics and its relation to applied linguistics as well as foreign language learning and teaching are visited, and several factors of psycholinguistic nature and their impacts of vocabulary learning are investigated. This paper makes some practical suggestions on how to deal with difficulties of learning English vocabulary from a psycholinguistic perspective while addressing each psycholinguistic factor at different sections.