Modeling the propagation of a Gaussian beam in a nanostructured gradient index microlens is reported. The nanostructured GRIN microlens is composed of subwavelength discrete dielectric rods. We compare the performance of nanostructured gradient index microlenses against conventional GRIN microlenses for Gaussian beam focusing. The 3D FDTD method is used for numerical analysis of optical systems. © 2010 Photonics Society of Poland.