By his senior year, he had lost interest in developing Chinese traditional painting and devoted himself to abstract expressionism.
加以當時對國畫發展的可能性感到失望，於是大學四年間都在畫西畫。民國四十五年從師大畢業以後，劉國松經營抽象水墨的趨勢便在意識中逐漸成形，但當時的表現形式和使用的材料，仍執著於油彩。