Abstarct: Precision seamless mextal tubes produced through rolling process are not perfectly straight due to application of asymmetric forming loads and presence of residual stresses. Since they have a three dimensional wavy axis, straightening of these tubes are problematic. Therefore, it is necessary to straighten them through a combined spinning and alternating bending process. This is usually done in a straitening machine which consists of multiple pairs of hyperbolic rolls. However, the straightening operation of the thin-walled tube depends mainly on the experience of operators and on the results of trials at present. This leads to a considerable waste and decease in production efficiency. This dissertation deals with the experimental and numerical study on the important parameters involved in thin walled tube straitening process. For a given straightening machine, these parameters roll velocity, roll eccentricity, roll angle and roll compression. The experiments were designed baxsed Taguchi method in MINITAB software. The experiments were conducted in two stages. The first set included four designs and the other consisted of one design. First design included 24 experiments and second design included 16 experiments. The second sets of experiments were designed baxsed on the results obtained from the first stage. Finally, some experiments were designed to verify the suggestions of the Taguchi model. In the numerical analysis, the explicit solver of Abaqus finite element package was used. In order to change the process parameters in the simulations, the parametric input file was developed and used. Parameters similar to the experimental ones were used in the simulations. The optimum conditions suggested by the experiments and simulations were compared. The experimental results show that the parameters which have the most influence on the final straightness of the tube in order of importance are roll compression, velocity, angle and eccentricity, respectively. The simulation results predict similar trend.