The fiber orientation distribution in fiber reinforced thermoplastics (FRP) affects the strength and the final shapes of products. Therefore, for effective product design using computer simulation, it is necessary not only to estimate the fiber orientation distribution, but also to mea-sure it. Although the fiber orientation has been measured using image analysis with soft X-ray photographs of thinly sliced FRP, only the 2D fiber orientation is obtained with these soft X-ray photographs. In recent years, a method to measure the 3D fiber orientation by using images of cut sections of FRP observed through scanning electric microscopy (SEM) has been reported. However, the azimuth angle of the 3D fiber orientation cannot be calculated. We thus propose a method to calculate the 3D fiber orientation by observing the elliptical marks and the interference fringe patterns in cut sections of FRP through scanning acoustic microscopy (SAM) in this paper. This method enables us to calculate the azimuth angle and measure the 3D fiber orientation in both the core layer and the skin layer. We show the effectiveness by measuring the 3D fiber orientation of a general cylindrical material.