Waste waters coming from three factories, namely Kuo tai (plastic), Shuang-shii (paper), and Chung-hwa (petroleum) were determined for their phytotoxicity and physicochemical properties. The effect of the waters on the growth and yield of rice (Oryza sativa Tainan 5) was also undertaken in pots. The bioassay results clearly showed that the waste waters exhibited significant phytotoxic effects on the radicle growth of rice, lettuce, and rye grass and suppressed the root initiation of mungbeans. Lettuce was the most sensitive species to waste water, rice the second, and rye grass the least. The phytotoxicity varied with monthly sampling and with every-four-hour sampling during a day. The quality and quantity of waste waters were different among three factories. Waste water coming from Kao-tai consistently revealed the highest toxicity upon these three plants, Chunghwa the second, and Shuang-shii the least. The original waste waters from the three factories showed significant inhibition on the rice growth, resulting in decrease in straw length, tiller number, panicle number, ripening rate, testing weight, and grain yield. The physicochemical analyses of waste water revealed that the amount of suspended solids, C1-, SO71 2 3, NH+-N, Na% Ca+2, Mg+a, and SAR, and the degree of electrical conductivity and osmotic concentration were significantly far beyond the standard criteria of irrigation water for agricultural land, and some of these properties would be severely detrimental to crop growth. Linear regression analyses showed that in some test waters the factors, such as electrical conductivity, suspended solid, CI-, SO,-4, NH+-N, and some cations were significantly correlated to the phytotoxicity.