Objective: The purpose of this study was to determine dental archs’ shape, and to describe differences in transversal dimensions and archs’ depths in mixed dentition, in order to know occlusal harmony arrangement in a native student population from Leticia, Amazonas, Colombia. Methods and Materials: A cross-sectional study with 64 students (32 boys and 32 girls) distributed in two groups: 31 students with early mixed dentitions and 33 students with belated mixed dentitions between 6 and 12 years old was carried out. Studied variables were measured from plaster cast study models. Results: Oval upper arch was found in 86% of students while 14% had squared upper arch. Proportions for lower arch shape were 75% oval and 25% squared, respectively. Most of the transversal dimensions had differences in both groups. Inferior intercanine distances were constant. Depth, width and length measurements are evidence of harmonic dental arch development for Amazonian children Discussion: This ethnic group had higher oval arch shape prevalence, followed by squared arch shape There were differences for all arch depth measurements, mainly in anterior sector due to the susceptibility to environmental factors in mixed dentition period. Conclusions: Occlusal harmony in this population is a result of arch shape, as well as transversal and depth changes