A common way to determine the electromagnetic properties of dielectric materials is to insert a sample of the material into a waveguide and measure the resulting reflection and transmission, i.e. the S-parameters. From the S-parameters the complex permittivity, e can then be extracted by use of various inversion schemes/algorithms, such as Nicolson-Ross-Weir (NRW) method. However, the NRW method is known to have inherently poor accuracy for high-permittivity materials. To mitigate this deficiency, here we propose an alternative approach for material parameter extraction. The novel method is based on measured S-parameter data and computational electromagnetics (CEM) simulation. In this method there is no restrictions on the shape and size of the material under test (MUT), as long as it fits in the waveguide and can be modeled with the CEM codes. In addition, the MUT does not have to be a single dielectric sample but it may be part of a combined metal/dielectric structure. We demonstrated this approach by measuring the complex permittivity of titanium dioxide (TiO 2 ) ceramic samples, with typical relative permittivity of 100.