The present research is concerned with studying nouns in English and their corresponding nouns in Arabic in order to determine some points of similarity and difference; particularly as far as number classes of nouns and their formation are concerned following the two descriptive models presented by Quirk, R., Sidney, G., Geoffrey, L., and Jan, S. (1985) for English and Aziz, Y. (1989)for Arabic. This research hypothesizes that forms of nouns are more complex, regular and productive in Arabic than nouns in English. In addition, the difference in the number classes of nouns and their formation in English and Arabic is due to the fact that English and Arabic belong to two different families. Thus, in order to provide a better insight in to the number classes and forms of the nouns understudy, the research consists of separate parts illustrating number classes and their formation in both English and Arabic. Then, a comparison of all the morphological techniques involved in forming number classes of nouns in both English and Arabic is highlighted and discussed expressing the points of convergence or divergence as far as the two languages are concerned. It is concluded that unlike English, Arabic nouns are governed by a large set of strict rules by means of which all classes of number are expressed with high accuracy and adequacy. Accordingly, the regularity and high efficiency of Arabic in producing an infinite number of plural nouns is an evidence for the high productivity of Arabic.