Photoaddition reactions of ο-benzoquinones to some organic molecules were ivestigated to yield three types of photoadducts. Irradiation (350nm UV light) of a dichloromethane solution of tetrahal-1, 2- benzoquinones and 1, 4-diphenylbutadiene yielded 1, 3-dienes, which was found to be used to synthesize 1-phenylphenanthrenes. The 1, 3-dienes were also produced, when irradiated tetrahalo--1, 2-benzoquinones and 1,4-dipenylbut-1-en-3-yne in the similar conditions, which was applied to get 9-phenylphenanthrenes. An enolic compound come from the tautomerization of dibenzoylmethane was found to add to ο-benzoquinones to give, 1, 4-dioxenes and 1, 5-diketones as the major products. Although depenylbutadiyne did not add to ο-benzoquinones, diphenylacetylene added to ο-benzoquinones to give $ ho$-quinomethanes as well as two isomeric $ ho$-quinomethanes. One-way photoisomerism was observed for two isomeric $ ho$-quinomethanes.