: In the current project, a Tailboom of a sample airplane was designed by topology optimization method and then the produced plan was optimized in order to reduce the mass as much possible.At first, topology optimization method is explained in this project. Then, airplane structure and its related forming materials along with airplane manoeuvre around its main axis are introduced. In the next step, the Tailboom of a light airplane is selected and modeled in CATIA software. In this model the Tailboom contains different parts: main body, horizontal stabilizer and vertical stabilizer. Then topology optimization is applied on this model with three different loading cases in finite element software ANSYS. These three loading cases are:1)imposed forces to horizontal stabilizers while taking off of the airplane,2)imposed forces on the horizontal stabilizer during the cruise airplane flight under vertical direction of wind and 3)imposed forces to horizontal and vertical stabilizer during the cruise airplane flight under side wind regime.By applying the topology optimization on this partial structure, the pass of the forces and overall shape of Tailboom is obtained. For investigating load paths as well as overall shape of the Tailboom, a pseudo density with values between 0 and 1 is considered for each element as the design variable. By relating stiffness of each element to this pseudo density and defining the minimum compliance as the objective function and the maximum volume fraction as the constraint, the elements which have a less structure related role are omitted during the optimization process to minimize the mass of the structure. Minimization compliance under multi-loading cases is a multidisciplinary optimization problem, since compliance of each loading condition is an objective function that should be minimized. In this work, weighted sum method that minimizes linear combination of objective functions is used for minimizing weighted sum compliance. But the value of each weight is determined by means of Pareto optimality concepts.By extracting and investigating the results of the topology optimization a conceptual plan was discovered and then modeled by BEAM element. At the last step, optimization processes, were applied on the obtained model by the method stated in the first step in order to reduce the weight. Finally, the optimized sections were rounded to the standard value according to DINEN10055, and then resolved and reanalyzed under the three loading cases.The result showed that small sections and uniform distribution of stress contours and also low value of stress and deflection of Tailboom structure validate the effectiveness and good performance of the topology optimization method in designing the structure. Keywords: Topology optimization, Optimization, Design, Airplane structure, Airplane Tailboom