SignificanceControlling the length of capsular polysaccharide (CPS) chains is thought to promote pathogen survival in various host niches. The polysaccharide copolymerase 2b family proteins were implicated in regulating CPS sizes. These proteins form a bacterial tyrosine kinase (BY-kinase) system that responds to the environment by modulating its phosphorylation status. Nevertheless, the role of autophosphorylation in capsule synthesis is still elusive. Here, we found that the disruption of BY-kinase CpsCD is lethal inStreptococcus pneumoniaeserotype 2 strain D39. Phosphorylation of CpsD resulted in shorter CPS polymers. We also provide cell biology evidence that CPS synthesis is coordinated with peptidoglycan synthesis.