3-Aminopropyltrimethoxysilane (3-APTMS) and 3-glycidoxypropyltrimethoxy-silane (3-GPTMS) mediated synthesis of gold nanoparticles (AuNPs) of two different sizes [AuNP1 (10 nm) and AuNP2 (20 nm)] were made and used for nano-composite formation with TiO2 nanoparticle suspension. The resulting TiO2-AuNP1 and TiO2-AuNP2 nanocomposites were used for making chemically modified electrodes to understand the role of nanogeometry in chemical sensing. TiO2-AuNP1 and TiO2-AuNP2 nanocomposites were characterized by transmission electron microscopy and UV-VIS spectroscopy. The analytical results revealed the average size of the nanocomposite in the range of 20-25nm. The nanocomposites were employed for modification of graphite paste electrodes and applied in electrochemical sensing of hydrazine. The results demonstrated that TiO2-AuNP1 exhibit better electrocatalytic activity as compared to that of TiO2-AuNP2 and only TiO2 towards oxidation of hydrazine. Amperometric analysis of hydrazine on these electrodes at the applied potential of 0.4 V vs Ag/AgCl was made to quantify the sensing ability of modified electrodes. The sensitivity and lowest detection limit was found as 25, 57.2 and 145.7 μAmM-1cm-2 and 50, 100, 20 nM for TiO2, TiO2-AuNP2 and TiO2-AuNP1 respectively.