A scissors bite is one of the more unusual malocclusions in primary dentition. The purpose of this report is to describe the unilateral scissors bite in primary dentition and the treatment outcome following the use of constriction appliances. A 5-year, 5-month-old boy developed a scissors bite in the left molar region due to the extended width of the maxillary dental arch. Two types of appliances were used to reduce the width of the maxillary dental arch; one was a removable type modified from a conventional expansion plate, and the other was a fixed type modified from a quad-helix appliance. The left maxillary primary molars were able to bite normally after the treatment using both appliances. As a result, the left first molars also could be guided to a normal occlusion and prevented from becoming a scissors bite. We suggest that improvement of the scissors bite in the primary dentition stage can prevent subsequent malocclusions in permanent dentition.