In this study, Graphene Quantum Dots (GQDs)/TiO2 nanocomposites were successfully synthesized by a simple, easy to implement method with a fast reaction time (30 min) and low reaction temperature (60o C). In particular, graphene quantum dots (GQDs) nanoparticles are obtained by green and environmentally friendly synthetic method using abundant and naturally available raw materials from rice starch and under supporting of microwave irradiation at power 900 W for 10 min. The synthesized GQDs were determined the morphology by Transmission electron microscope (TEM) with average particle size ~8-15 nm. In addition, the synthesized GQDs were successful combined with TiO2 nanoparticles (TiO2 NPs) to form GQDs/TiO2 nanocomposites with highly optical property and photocatalytic activity. These GQDs/TiO2 nanocomposites synthesized were also analyzed their characterizations, morphologies and compositions by: UV-vis, FTIR, XRD, TEM and EDX. Results showed that GQDs/TiO2 nanocomposites were spherical in shape, with average particle size of ~10-25 nm; and their components obtained including: C (41.36%); O (54.08%); and Ti (4.56%), respectively. Moreover, these GQDs/TiO2 nanocomposites were also applied in the detection of Chromium(VI) ions with lowest limit of detection (LOD) for Chromium(VI) ions concentration being ~0.1 µM and in the wide detection range from 0.01 M to 0.1 µM by photoluminescence spectroscopy (PL). Therefore, the obtained GQDs/TiO2 nanocomposites have potential to be developed as photocatalyst materials applications in many fields such as sensors, biosensors, sensors, biomedical, optoelectronics, etc.