NOVELTY - A silicon-containing curable composition comprises prepolymer (A) having two or more silyl groups per molecule, and linear siloxane compound (B) (I). The prepolymer (A) is obtained by hydrosilylating at least one cyclic siloxane compound (a) (II) and at least one compound (b) chosen from group (i)-(vii).    USE - Silicon-containing curable composition is used for cured material (claimed) including insulating film, electrical/electronic material, passivation film, sealing material, low-dielectric constant material, adhesive material, heat-resisting material and transparent material. Uses include but are not limited to display material, optical material, recording material, semiconductor, solar cell, prepreg, insulation packing material, optical fiber protective material, optical lens, fuel cell component, etc.    ADVANTAGE - The silicon-containing curable composition has excellent adhesiveness, transparency and colorability. The cured material containing silicon-containing curable composition has excellent crack resistance, weather resistance, contamination resistance, flame resistance, moisture resistance, gas barrier property, flexibility, elongation, low-dielectric property, optical characteristic, electrical property and strength.    DETAILED DESCRIPTION - A silicon-containing curable composition comprises prepolymer (A) having two or more silyl groups per molecule, and linear siloxane compound (B) of formula (I). The prepolymer (A) is obtained by hydrosilylating at least one cyclic siloxane compound (a) of formula (II) and at least one compound (b) chosen from group of formula (i)-(vii).    R1-R3=phenyl optionally substituted by 1-6C alkyl, or 1-6C alkyl;    a=2-10;    b=0-8;    R4-R6=H, 1-10C alkyl, 2-10C alkenyl, 2-10C alkenyloxy, 2-10C epoxy, or phenyl optionally substituted by 2-10C alkenyl, 3-10C acryl or 2-10C epoxy, where two of R4, R5 and R6 are substituents having carbon-carbon double bond;    m,n=1 or 2;    R13,R32=trimethyl-silyl, or group having 2-6C alkenyl, 1-6C alkyl or 2-10C epoxy;    R14-R17,R21,R25,R29-R31=H or 1-6C alkyl;    R18-R20=phenyl;    R22-R24=2-6C alkenyl;    R26-R28=group having 2-10C epoxy;    Z1-Z8=single bond, 1-10C alkylene, phenylene or O;    p-r,v-y=0-3000;and    p+q+r+v+w+x+y=1 or more.    (i) When R13 and R32 are 1-6C alkyl, v is 1 or more or v+w is 2 or more; and (ii) When at least one of R14-R17, R21, R25 or R29-R31 is H, v is 1 or more or w is 1 or more. An INDEPENDENT CLAIM is included for cured material, which is obtained by hardening silicon-containing curable composition.