Plastic tubes and hollow rods can be fabricated using gas-assisted injection molding technology with reduced cost. The residual wall thickness around dimensional transitions and curved sections is of great concern. This research investigated the uniformity of the residual wall thickness distribution in circular tubes with dimensional variations and curved sections. It was found that the wall thickness was not uniform near transitions. With the addition of fillets with proper angles around transitions, the uniformity of residual wall could be greatly improved. The residual wall thickness in curved sections was thick around the outer wall and thin around the inner wall. Low melt temperature and high gas pressure were found to reduce the deviation in the wall thickness around curved sections.