In this study, the effect of using of titanium dioxide-water (TiO2/ water) nanofluid on the performance of the flat plate solar collector (FPSC) has been experimentally investigated. The nanofluid was obtained by mixed with a 2 wt% TiO2/pure water mixture. In order to maintain the stability of the prepared nanofluid suspension and to eliminate the problem of agglomeration over time, 0.2 wt% Triton X-100 surfactant was added into the mixture. The nanofluid was mixed in continuous pulsing for 8 h in ultrasonic bath. In the experiments done in accordance with EN ISO 9806 standard, the highest instantaneous enhancements for pure water and nanofluid was determined and the results were provided by graphical representations comparatively. In the experimental flat plate solar collector setup, the highest instantaneous efficiency was obtained to be 48.67% for TiO2/water nanofluid, whereas the highest instantaneous efficiency was 36.20% for pure water.