Disclosed are a curable polysiloxane composition for an optical device includes at least one of a first siloxane compound represented by the following Chemical Formula 1, at least one of a second siloxane compound having silicon-bonded hydrogen (Si—H) at the terminal end, and at least one of a third siloxane compound having a silicon-bonded alkenyl group (Si-Vi) at the terminal end, an encapsulant obtained by curing the curable polysiloxane composition for an optical device, and an optical device including the encapsulant. (R1R2R3SiO1/2)M1(R4R5SiO2/2)D1(R6R7SiO2/2)D2(R8SiO2/2—Y1—SiO2/2R9)D3(R10SiO3/2)T1(R11SiO3/2)T2(R12SiO3/2)T3(SiO3/2—Y2—SiO3/2)T4(SiO4/2)Q1  [Chemical Formula 1] In the above Chemical Formula 1, R1 to R12, Y1, Y2, M1, D1, D2, D3, T1, T2, T3, T4 and Q1 are the same as defined in the specification.