Novel sensor for dissolved oxygen (DO) centered on ternary composite of graphene/titanium dioxide/silver nanoparticle (G-TiO2-Ag) enhanced glassy carbon electrodes can be investigated. This modified composite was created using a hydrothermal process and then placed on the surface of the glassy carbon (GC) electrode as an active material. The electrochemical behavior of the GC/G-TiO2 modified electrode in 0.1 M PBS displayed two steps four electrons (4e`) mechanism for DO reduction, while, the electrochemical behavior of GC/G-TiO2-Ag displayed only one obvious peak which strongly indicates a fast and efficient one step (4e`) mechanism for DO reduction. A higher reduction current is obtained for DO on GC/G-TiO2-Ag compared with that on GC/G-TiO2 reflects a synergistic effect between Ag and TiO2. The amperometric measurement showed two linear regions, the first one is from 1 to 30.29 µM with sensitivity of 1.363 µAcm-2 µM-1 and detection limit of 0.011 µM (signal/noise = 3/1) and a correlation coefficient of 0.996. The second linear region shows an increase in response, with low rate than the first region, for DO concentration up to 100 µM (correlation coefficient 0.990) with sensitivity of 0.725 µAcm-2 µM-1 and detection limit of 0.214 µM.