Abstract: The present invention relates to novel 4,5-dihydro-6H-imidazo[4,5,1-ij]quinolin-6-one-6-oxime-O-sulfonic acid compounds, processes for producing said compounds, intermediate compounds, i.e. novel 4,5-dihydro-6H-imidazo[4,5,1-ij]quinolin-6-one compounds and 4,5-dihydro-6H-imidazo[4,5,1-ij]quinolin-6-one-6-oxime compounds in the synthesis of said compounds, processes for producing said intermediate compounds, and pharmaceutical or veterinary compositions containing said compounds.The present invention is based on the selection of the substituents of 4,5-dihydro-6H-imidazo[4,5,1-ij]-quinolin-6-one-6-oxime-O-sulfonic acid compounds at 2-position, namely 2-(2-penten-3-yl)-, 2-cyclohexyl-, 2-naphthyl-, 2-thienyl-, etc.The compounds of the present invention containing these substituents have potent hypotensive, anti-oedematous and diuretic effects as well as an activity of removing ascites. The compounds of the present invention are extremely useful for treatment of diseases and disorders mentioned above.