This study developed and validated a Primary School Mathematics Motivation Scale (PSMMS) to measure motivation of primary school students towards learning mathematics. An initial 74-item scale was administered to 347 third and fourth grade students. Exploratory factor analysis revealed the scale measured a single factor explaining 42.46% of the variance. 33 items with loadings above 0.50 on this factor were retained in the final scale. The scale demonstrated good reliability with a Cronbach's alpha of 0.94. The results indicate the PSMMS is a valid and reliable measure of primary school students' motivation in mathematics that can be used in future educational research.