Selective catalytic reduction (SCR) is currently the most effective method to control NO_x emissions for heavy-duty vehicles. However, urea-water solution injection may lead to increase of particulate matter (PM) emissions. In this study, PM emissions caused by urea-water solution injection from a China VI heavy-duty vehicle under real-world driving conditions is investigated experimentally. Average PM number emissions increase by over 200% due to urea-water solution injection. Inlet temperature and space velocity are found to be significant factors. Droplet depletion model is developed for analyzing the contribution of urea decomposition by-products. Results suggest that secondary-breakup-based particles is major contributor to particles formation instead of primary-breakup-based. About 20% of secondary-breakup-based particles are nuclei mode particles and 80% are accumulation mode particles. The main component of the secondary-breakup-based particles is cyanuric acid and ammelide.