The concept of 3-dimensional (3D) modeling by an autonomous mobile robot is presented. The mobile robot is equipped with a stereo camera and explores an unknown environment autonomously. The robot also has encoders and sonars. Information from these sensors are used for 3D modeling, ego-motion, and searching new and unknown objects. The 3D modeling of real environments by a mobile robot is applicable to optimal path planning, object recognition, virtual reality (VR), and so on. A preliminary result of the 3D modeling is also shown.