MEMS (MicroElectroMechanical Systems) are composed of thin films and composite nanomaterials. Although the mechanical properties of their constituent materials play an important role in controlling their quality, reliability, and lifetime, they are often found to be different from their bulk counterparts. In this paper, low-k porous silica thin films spin coated on silicon substrates are studied. The roughness of spin-on coated porous silica films is analyzed with in-situ imaging and their mechanical properties are determined using nanoindentation. A Berkovich type nanoindenter, of a 142.3 deg total included angle, is used and continuous measurements of force and displacements are acquired. It is shown, that the measured results of hardness and Young’s modulus of these films depend on penetration depth. Furthermore, the film’s mechanical properties are influenced by the properties of the substrate, and the reproduction of the force versus displacement curves depends on the quality of the thin film. The hardness of the studied low-k spin coated silica thin film is measured as 0.35∼0.41 GPa and the Young’s modulus is determined as 2.74∼2.94 GPa.