Nanotechnology has become an emerging field to harness solar energy. Nanoparticles are of particular interest due the diversity of structural motifs and morphologies and applications. Solar energy is the most abundant source of renewable energy which can be an everlasting solution to energy crisis. The aim of this study was to synthesize Cobalt oxide and Cobalt sulphide nanoparticles for harvesting solar thermal energy. To synthesize Cobalt oxide (Co2O3) nanoparticles, CoCl2. 6H2O (4 g) was dissolved in distilled water. Then, 6 mL ammonia solution was added drop by drop into the salt solutions. The mixture was stirred for 3-hours, filtered and cleaned with water. Then to remove chloride impurities, the precipitates were dried in an oven at 100°C. The dried precipitates were calcined in the furnace at 450°C for five hours. Similarly, for the preparation of cobalt sulfide nanoparticles, equimolar quantities of cobalt(II) salt solution and sodium sulfide solution in distilled water was sonicated for 2 hrs. Formation of black precipitate confirmed the formation of nanoscale cobalt sulfide. Further, nanoparticles were characterized by UV-Visible spectroscopy. Moreover, the cobalt oxide and cobalt sulphide nanofluids exhibited excellent solar thermal activity and gave successful results.