In this article, an improved grey wolf optimizer (IGWO) algorithm is developed for optimal design of truss structures. Grey wolf optimizer (GWO) is a recently proposed algorithm for optimization, which is herein improved to handle structural optimization in an efficient manner. In this work, performance of the GWO in structural optimization is also investigated. A few tunable parameters are defined to provide proper adaptability for the algorithm and to optimize the structures using fewer structural analyses, while obtaining finer solutions. Hence, in addition to reduce the computational efforts, better solutions are obtained as it is shown by several benchmark examples, where both GWO and IGWO are employed for the optimization. Mathematical functions as well as various design examples from small to large truss structures with different search spaces are examined to demonstrate the ability and efficiency of the present improved version in comparison to its standard version.