This investigation explores the contribution of three working memory systems (the phonological loop, the visuo-spatial sketchpad, and the central executive) to the performance differences of sentence comprehension between children with Williams syndrome (WMS) and typically developing children. When 12 children with WMS and 12 typically developing children, matched in the size of acquired lexicon, were tested on a sentence-picture matching test containing nine different sentence types representing different level of syntactic complexity, overall performance of children with WMS was poorer than typically developing children. However, children with WMS showed normal effect of phonological variable as span, and exhibited even better performance than typically developing children on a measure of phonological processing accuracy. On the other hand, children with WMS had reduced visuo-spatial span in the executive system and showed poorer performance than typically developing children on a measure of visuo-spatial accuracy. These findings are argued in terms of the characteristics of language learning of WMS children.