BACKGROUNDS. Chewing is a cyclic mandibular movement on the functional teeth surfaces that prepares the bolus for swallowing with the help of the related nerves, muscles and soft tissues in the oral cavity. The time and surface of the chewing cycle in adults considerably differs from the chewing cycle in children. The growth and development of the orofacial system in children have a significant impact on changes in the chewing cycle. METHODS. The research study included 31 children (17 boys, 14 girls) aged 4-6 years (5.42 years on average) during the period of deciduous dentition. The measurements were repeated after a year and a half in the same children who at that time were aged 5.5-7.5 years (6.92 years on average), after the eruption of their first permanent molars. The chewing cycles were measured using an elec- trognathographic device Sirognatograf (Siemens, Germany). Data collection and analyses were performed with the COSIG II software. The mandibular movements were monitored in the frontal and sagittal planes. The parameters of the chewing cycles were measured and analysed regarding shape and duration. RESULTS. In the frontal plane, the surface area of the chewing cycles increased from 21.92 mm2 to 33.68 mm2, while in the sagittal plane, it increased from 3.08 mm2 to 9.53 mm2. The average opening time per individual chewing cycle was extended (from 0.21 s to 0.28 s), resulting in a prolonged duration of the whole chewing cycle (from 0.6 s to 0.7 s). CONCLUSIONS. The obtained results confirmed our hypothesis that, upon the eruption of the first permanent molars, the first bite raise has a significant impact on changes in chewing. The surface area of the chewing cycle in the frontal and sagittal planes is also enlarged. During the period of mixed dentition, the duration of mouth opening is prolonged, and this has an impact on the time component of the total chewing cycle.