A sentence is constructed using basic word units. Each word is composed of syllables and each syllable being composed of phonemes, which in turn, can be classified as vowels or consonants. Vowels may occupy the center or nucleus of a syllable, as opposed to consonants, which occur in marginal positions in a syllable (onsets and codas).Vowels appear early in speech development and are central to understanding the acoustic properties of speech. The aim of this work is to enrich the automatic speech recognition system, by the classification of Arabic vowels based on normalized energy in the formant frequency bands.