Given the rich bound morphology of Spoken Arabic, an attempt was made here to construct a developmental measure corresponding to the mean length utterance (MLU) in English and to morpheme-per-utterance (MPU) in Hebrew. The adaptation to Arabic resulted in a new measurement termed Arabic-MPU, that was experimentally tested on a sample of 98 typically developing (TD) Arabic-speaking preschoolers aged 2;6 to 5;0. We report here on the internal consistency of Arabic-MPU against different types of elicitation procedures, and its external validity. We show that the new tool is developmentally sensitive and hence can be utilized for the assessment of the language growth in Spoken Arabic. This new tool should contribute to further research and development of measures for language assessment. In addition, it can be used for language screening in preschoolers for the purpose of identifying young speakers of Arabic who exhibit delays in early language development.