Disclosed is a solution composition for forming a thin film transistor including a zinc-containing compound, an indium-containing compound, and a compound including at least one metal or metalloid selected from the group consisting of hafnium (Hf), magnesium (Mg), tantalum (Ta), cerium (Ce), lanthanum (La), silicon (Si), germanium (Ge), vanadium (V), niobium (Nb), and yttrium (Y). A method of forming a thin film by using the solution composition, and a method of manufacturing thin film transistor including the thin film are also disclosed.