NOVELTY - A pyrimidine derivative (I) is new.    USE - The pyrimidine derivative is useful in agrochemical composition used as herbicide for controlling weeds in agriculture (all claimed), and for crops and useful plants such as maize, rice plant, wheat, barley, rye, oats, sorghum, cotton, soybeans, peanut, buckwheat, sugar beet, rapeseed, sunflower Helianthus annuus, sugarcane, and tobacco, Solanaceae vegetable (eggplant, tomato, green pepper, red pepper, potato, etc.), cucurbitaceous vegetable (cucumber, pumpkin, zucchini, watermelon, melon, etc.), Brassicaceae vegetable (Japanese radish, turnip, horse radish, kohlrabi, and Chinese cabbage, mustard, broccoli, cauliflower, etc.). The weeds include Onagraceae weeds e.g. Oenothera erythrosepala Ranunculaceae weeds e.g. Ranunculus muricatus, Polygonaceae weeds e.g. Polygonum convolvulus, Polygonum lapathifolium, Polygonum pensylvanicum, Polygonum persicaria, Rumex crispus, Rumex obtusifolius, Poligonum cuspidatum, Polygonum pensylvanicum, Persicaria longiseta, Persicaria lapathifolia, and Persicaria nepalensis, Portulacaceae weeds e.g. Portulaca oleracea, Caryophyllaceae weeds e.g. Stellaria media, Cerastium glomeratum, Stellaria alsine, Spergula arvensis, and Stellaria aquatica, Chenopodiaceae|Amblycipitidae weeds e.g. Chenopodium album, Kochia scoparia, Chenopodium album, and Chenopodium ficifolium, Amaranthaceae weeds e.g. Amaranthus retroflexus, Amaranthus hybridus, Amaranthus palmeri, Amaranthus spinosus, Amaranthus rudis, Amaranthus albus, Amaranthus viridus, and Amaranthus lividus, and Brassicaceae weeds wild radish (Raphanus raphanistrum), and Sinapis arvensis.    ADVANTAGE - The pyrimidine derivative shows excellent herbicidal property for long period of time, even at low dose and is environmentally-friendly.    DETAILED DESCRIPTION - A pyrimidine derivative of formula (I) is new.    R1=H, 1-12C alkyl, 2-6C alkenyl, 2-6C alkynyl, 3-6C cycloalkyl, 3-6C cycloalkenyl, 3-6C cycloalkyl-1-6C alkyl, 1-6C haloalkyl, 2-6C haloalkenyl, 2-6C haloalkynyl, 3-6C halocycloalkyl, 3-6C halocycloalkyl-1-6C alkyl, amino-1-6C alkyl, nitro-1-6C alkyl, (R31R32N-C=O)-1-6C alkyl, NR31R32, 3-6C cycloalkyl-1-6C alkyloxy or 1-6C haloalkoxy;    R2=1-6C alkyl, 2-6C alkenyl, 2-6C alkynyl, 3-6C cycloalkyl, 1-6C haloalkyl, 2-6C haloalkenyl, di(1-6C alkoxy)-1-6C alkyl or 3-10C heterocyclyl;    Y',Z=O or S;    A=group of formulae (a)-(e);    R4=phenyloxy, benzyloxy, hydroxy, O-M+, amino, halo, cyano, isothiocyanate, isocyanate, 2-6C alkynylthio, 2-6C alkynyl sulfinyl, 2-6C alkynyl sulfonyl, 1-10C alkylamino, di(1-10C alkyl)amino or 1-6C alkoxy carbonylamino;    M+=alkali-metal cation or ammonium cation;    A1=-C(-R5)(-R6)- or -N(-R7)-;    A2=-C(-R8)(-R9)-, -C(=O)-, -S(=O)n-, -O- or -N(-R33)-;    A3=-N(-R34)- or -C(-R35)(-R36)-;    n=0, 1 or 2;    R5,R6,R8,R9,R35,R36=H or 1-6C alkyl;    R7,R33,R34=H, 1-6C alkyl, 1-6C haloalkyl, 2-6C alkenyl, 2-6C alkynyl or 1-6C alkoxy;    R14-R17=benzyl, H, 1-6C alkyl or 1-6C alkoxy;    R18=H, 1-6C alkyl, 2-6C alkenyl, 2-6C alkynyl, cyanomethyl or benzyl;    R20=1-6C alkyl, 2-6C alkenyl, 2-6C alkynyl, 3-6C cycloalkyl or 3-6C cycloalkyl-1-6C alkyl;    R21=H, 1-6C alkyl or halo;    R23=phenylthio, benzylthio, phenylsulfinyl, benzylsulfonyl, phenylsulfonyl, benzylsulfinyl, 1-6C alkyl, 1-6C haloalkyl, 3-6C cycloalkyl, 1-10C alkylthio, 1-10C alkylsulfinyl or 1-10C alkylsulfonyl;    R24=H, halo, cyano, 1-6C alkyl, 3-6C cycloalkyl or 1-6C alkoxy carbonylamino;    R25=1-6C alkoxycarbonyl, cyano or nitro;and    R31,R32=phenyl, benzyl, phenylsulfonyl, benzylsulfonyl, 3-10C heterocyclyl, H, 1-6C alkyl, 1-6C alkoxy-1-6C alkyl, 1-6C alkylcarbonyl, 1-10C alkylthio carbonyl, 1-6C alkoxycarbonyl, 1-6C haloalkyl, 3-6C cycloalkyl, 3-6C cycloalkyl-1-6C alkyl or 1-6C alkylsulfonyl.    "Full Definitions are given in the DEFINITIONS (Full Definitions) field with specified proviso".