The photooxidation of diphenylamine is acetonitrile and methanol using Hypocrellin A as sensitizer will be reported in this paper. The products in the two solvents were isolated and identified. The reaction mechanisms were investigated. In acetonitrile, diphenylamine was oxidized by singlet oxygen to form N-phenyl-p-benzoquinonimine. In methanol, N-phenyl-p-benzoquinonimine was produced predominantly through a mechanism irrelevant to singlet oxygen. A small amount of diphenylamine reacted with methanol and singlet oxygen to give a novel product: N-phenyl-2-methoxy-p-benzoquinonimine.