Number sense, an integral part of the curriculum in primary school mathematics, has always been thought of as playing a major role in pupils' understanding and use of numbers in calculation. Research in number sense has been carried out in the West, as well as in Malaysia. That a study of such a nature be done to reflect on the abilities of primary school pupils in this area, the authors embarked on the development of an instrument to assess pupils' number sense. The instrument constructed focused on counting, addition and subtraction, multiplication and division, and place value, but this study examined pupils' abilities in multiplication and division. The responses obtained after administering the instrument to 128 pupils were analyzed and the authors found the instrument to be suitable for measuring the acquisition of number sense with respect to multiplication and division. (Contains 4 figures and 1 table.)