In the present paper a new, very simple, rapid and economical qualitative technique is being reported. By means of this technique, adulteration of argemone oil in mustard oil can be detected. In the test, a small quantity of suspected oil successively treated with phenol and conc. sulphuric acid a deep red colour develops. Development of red colour in above test is due to formation of quinonoid compound and hydrolysed sanguinarine salt which indicates the presence of argemone oil as adulterant in test sample. Up to 0.05% argemone oil adulteration can be detected with the new technique.