NOVELTY - A room-temperature hardenable polyorganosiloxane composition is 2-component composition comprising main ingredient composition, and curing agent composition. The main ingredient composition comprises polyorganosiloxane (a) in which molecular chain terminal is blocked with hydroxyl group, filler (b), and polyorganosiloxane (c) having an average unit (I).The curing agent composition contains trifunctional or tetrafunctional silane compound (II) or its partial hydrolysis-condensation product (e) and amino-group-containing silicon compound (f) (III) and/or (IV).    USE - Room-temperature-hardenable polyorganosiloxane composition. Uses include but are not limited to solar component, motor vehicle component, electrical/electronic device component, potting material, coating material, formed in place gasket sealing material, sealing material for construction, and on-site formation gasket.    ADVANTAGE - The room-temperature hardenable polyorganosiloxane composition has excellent hardenability, hydrolysis resistance and adhesiveness with respect to base material, and provides hardened material having excellent hardness even at high-temperature and high-humidity.    DETAILED DESCRIPTION - A room-temperature hardenable polyorganosiloxane composition is a 2-component composition comprising a main ingredient composition, and a curing agent composition. The main ingredient composition comprises 100 parts mass polyorganosiloxane (a) having viscosity of 0.1-100 Pa.second at 23 degrees C in which molecular chain terminal is blocked with hydroxyl group, 1-300 parts mass filler (b), and 0.1-20 parts mass polyorganosiloxane (c) having an average unit of formula: (R13SiO1/2)p(Si(OH)xO(4-x)/2)q (I). The curing agent composition comprises 0.1-20 parts mass trifunctional or tetrafunctional silane compound of formula: R2nSi(OR3)4-n (II) or its partial hydrolysis-condensation product (e), 0.1-20 parts mass amino-group-containing silicon compound (f) of formula: (R4O)3Si-R5-NH-R6 (III) and/or of formula: (R7O)3-mR8 mSi-R9-NH-R9-SiR8l(OR7)3-l (IV), and 0.01-10 parts mass tin-type curing catalyst (g).    R1=1-20C monovalent hydrocarbyl;    x=0.001-0.8;    p,q=positive number;    R2,R8=optionally substituted monovalent hydrocarbyl;    R3,R4,R7=unsubstituted monovalent hydrocarbyl;    n=0 or 1;    R5,R9=optionally substituted bivalent hydrocarbyl;    R6=H, unsubstituted monovalent hydrocarbyl, or aminoalkyl;and    m,l=0-2.