Background: Measurement of normal maximum mouth opening (MMO) in children is an important diagnostic criterion in the evaluation of the stomatognathic system. The aim of this study was to determine the MMO in children from the Indian population, of age six to twelve years, and to examine the possible influence of age, gender, height, and body weight on MMO. Assessment of MMO was accomplished with a modified Vernier Caliper, by measuring the distance between the incisal edges of the upper and lower incisors during maximal mouth opening up to the painless limit. Materials and Methods: The study consisted of 856 children from various schools in the city of Rohtak (Haryana), India, who were randomly divided into three groups based on their age: Group 1: Children of age six to eight years; Group II: Children of age eight to ten years; Group III: Children of age ten to twelve years. For each subject three readings were recorded in millimeters and the mean value was considered. The age, gender, height, and body weight of each child were also recorded at the same time. A P value of < 0.05 was considered to be significant. Results: The results of the present study revealed that MMO in Indian children were 46.04 mm, 48.53 mm and 52.38 mm for boys and 45.95 mm, 47.27 mm and 52.05 mm for girls, in the age groups of six to eight, eight to ten, and ten to twelve years, respectively. Conclusion: Significant associations were observed in between age, height, body weight, and MMO. However, no gender difference was observed.