A familiar phonotactic constraint in Arabic limits mono-syllabic words to CVVC and CVCC syllable type, where VV and CC are long segments. In this study, we are interested in learning, first, whether vowel length difference serves as a perceptual cue of the length difference between short (single) and long (geminate) consonants. Second, if consonant length difference cues vowel length difference. Spectrographically analyized data on the two features: vowel length and consonant length were prepared for the purpose of this perception study. To provide developmental data, two groups of native Arabic speakers were recruited to serve as subjects, adults and children. Findings of this perception study indicate that vowel duration and consonant duration differences of length contrast are useful perceptual cues of consonant length and vowel length, respectively. Moreover the children subjects have shown more or less the same sensitivity to the three acoustic parameters of vowel length, consonant length and voice as the adults. Findings of the experiment in question will be taken up for discussion in regard of their consequences for models of phonetic control and syllable structure. (Research supported by Yarmouk University).