In helicopters, the rotor blade structural dynamic characteristics play an important role in the overall performance of the vehicle, defined in terms loads, vibration and handling qualities. The placement of natural frequencies in flap and lag is a critical step in the design of a practical rotor blade. A systematic optimization procedure in the design of cross sectional variations of structural and inertial properties will greatly help in the design process. An optimization procedure developed for the placement of natural frequencies in a non-uniform rotor blade is presented in this paper. The first flap and the first lag natural frequencies are considered for the optimization. A single cell section is selected for the blade root cross section in this study. The wall thickness of the single cell section is selected as primary design variable. The secondary design variables, stiffness and structural mass properties are modelled as parametric equations of the primary design variable. In this work the constraints are imposed on minimum wall thickness to cater for axial stress due to centrifugal force. A gradient based method along with the interior penalty function is used for the optimization. To automate the complete optimization process, the optimization program is linked with the computational tools Cross Sectional Properties Evaluation (COPE ) and Structural Dynamics Analysis of Rotor Blade (SDAR). These codes are developed at Helicopter Lab of Aerospace Engineering department, IIT Kanpur and validated with experimental data. © 2016, American Helicopter Society International. All rights reserved.