First permanent molar mandible had already errupted in  6-7 years old and the root formation completes at age of 9-10 years. The root formation of first permanent mandible starts at 5 years and 3 months old, which in radiograph shows as radiopaque area that appear below the crown line, and the root development become half of the root formation at 6 years and 2 months old. This stage of first permanent mandible root development can be associated with age estimation. The aim of this study was to determine the stage of the root development, the shape and lenght of the first permanent molar mandible in children aged 6-10 years old in periapical radiograph. The radiograph was placed on the viewer box and marked the edge of cemento enamel junction and the tip of apex root by pencil and placed the tip of calipper on the two point that have been marked then measured the leght using a ruler. Measurement of the roots length were taken for mesial and distal of each tooth and noted the root shape that assessed form the radiograph. The result of this study shown that the lenght of first permanent mandible of 6-10 years old was in the range of 5,5 -14 mm for mesial root an 4,5 – 12 mm for distal root. The majority of root development shape was at stage R ¾ at 6 years (71,4 %), at 7years (100 %), at 8 years (85,7%) and at the age of 9 years old 85,7% of root shape was at stage Rc and 57,1 % of the rooot shape of the 10 years old was at stage Ac, which stage means the root formation already complete. As a conclusion, the mesial root length appears longer than the distal length with the root lenght varies on the age of 6-10 years old. The root development shape of 6 and 7 until 8 years old mostly shows the root already formed ¾ of root formation, then at 9 years old the root shape become complete but the apex not yet, and at 10  years  old the stage of the root shape already complete which shown by the closed of the root apex completly.