Sol-Gel derived thin films are becoming increasingly important for optical sensor applications. Analyte-sensitive dyes are easily entrapped in the porous film while remaining accessible to the analyte, and the nature of the sol-gel process lends flexibility to film fabrication, in particular enabling tailoring of film properties for specific sensor applications. Recent work has indicated the ormosil films, fabricated from organically modified precursors, produce better sensor performance for some specific applications, compared to films from conventional sol-gel precursors such as tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS). This project aims to compare film properties and sensor behaviour for films fabricated from different organically modified precursors. Microstructural differences, for example porosity changes due to the different precursor backbone structures, are investigated by monitoring sensor response. Sol-Gel fabrication parameters such as sol pH and R-value are varied. Resulting film properties such as thickness, thickness stabilisation time and sensor response are discussed in terms of relative hydrolysis and condensation behaviour for the different precursors. Issues that have been identified as being of crucial importance for optimum sensor response, such as dye leaching, film surface hydrophobicity and humidity response are discussed for both film types. The motivation for this work is film optimisation for optical sensors in particular gas phase and dissolved oxygen sensors.