NEW MATERIAL: A substituted uracil represented by formula I (wherein R1 is an aromatic or a heteroaromatic; R2 is H, an alkyl, an alkenyl, an alkynyl or an aralkyl; R3 is H, a halogen, an alkyl, a halogenoalkyl, an alkoxyl, an alkylthio, a halogenoalkoxyl a halogenoalkylthio, cyano or the like; R4 is H, an alkyl, an alkenyl, an alkynyl or an aralkyl).

EXAMPLE: 2,6-Dichloro-α-(4-chlorophenyl)-4-(1-uracil)phenylacetonitrile.

USE: A controlling agent of parasitic protozoa on an animal.

PREPARATION: For example, a novel compound of formula II (wherein Alk is a 1-4C alkyl) is heated in the presence of optionally a base to obtain a substituted uracil of formula I.