The invention provides a technique for manufacturing a high-titanium-content feedstock by efficiently separating out and removing metal impurities from a titanium-containing feedstock such as titanium slag or ilmenite. A method for improving the quality of a titanium-containing feedstock is also provided. In said method, impurities in a titanium-containing feedstock that contains slag are selectively separated out and removed as chlorides, yielding a high-titanium-content feedstock. Said method is characterized in that the titanium-containing feedstock is subjected to an oxidation treatment prior to selective chlorination. Also, in this method, the oxidation treatment and the selective-chlorination treatment are performed simultaneously.