Discussed are an ink containing nanoparticles for formation of thin film of a solar cell and its preparation method, CIGS thin film solar cell having at least one light absorption layer formed by coating or printing the above ink containing nanoparticles on a rear electrode, and a process for manufacturing the same. More particularly, the above absorption layer includes Cu, In, Ga and Se elements as constitutional ingredients thereof and such elements exist in the light absorption layer by coating or printing an ink that contains Cu2Se nanoparticles and (In,Ga)2Se3 nanoparticles on the rear electrode, and heating the treated electrode with the ink. Since Cu(In,Ga)Se2 (CIGS) thin film is formed using the ink containing nanoparticles, a simple process is used without requirement of vacuum processing or complex equipment and particle size of the thin film, Ga doping concentration, etc., can be easily regulated.