This paper presents the pose estimation of the small UAV utilizing only low cost cameras installed indoor. To overcome the limitation of the outside flight experiment, the multi-camera indoor test-bed is developed, which consists of four major components : the multi-camera, the ground computer, the onboard color markers, and the UAV. The dynamic model of the small UAV is the six-degrees-of-freedom nonlinear equations and the measurements are the visual information of marker attached to the UAV which is obtained periodically by the camera. The unscented KALMAN FILTER (UKF) is used to obtain an accurate position and pose estimation for the small UAV. This paper finishes with several experiment results illustrating the performance and properties of the proposed multi-camera system and vision algorithm.