Zinc and lactase deficiency are closely associated with the severity of gastroenteritis in children. Absorption of lactose is dependent on lactase and enhances the absorption of zinc. In the present study, we analyzed the association of the lactase (LCT)-13910 polymorphism and serum zinc levels with the severity of gastroenteritis in Korean children. 133 gastroenteritis patients and 476 healthy controls were examined for their LCT-13910 genotype using a polymerase chain reaction-restriction fragment length polymorphism. We also analyzed serum zinc levels in 111 pediatric patients and compared their severity of gastroenteritis. For the LCT-13910 genotype, all of 133 gastroenteritis patients and 476 healthy children had only the C/C genotype, which is associated with lactase deficiency. In addition, 111 pediatric patients showed no deficit of serum zinc and no association with severity of gastroenteritis. These results suggested that LCT-13910 polymorphism and zinc deficit may not be risk factors and that zinc administration may not be needed in Korean pediatric patients with gastroenteritis.