The present invention provides a sealant for an optical semiconductor device which has high gas barrier property against corrosive gas, and is less likely to crack or is less likely to peel off even when used in harsh environments.The sealant for an optical semiconductor device includes: a first silicone resin component including at least one of a first silicone resin A represented by formula (1A) shown below and a first silicone resin B represented by formula (1B) shown below, the first silicone resin A not containing a hydrogen atom bound to a silicon atom, but containing an aryl group and an alkenyl group, the first silicone resin B not containing a hydrogen atom bound to a silicon atom, but containing an aryl group and an alkenyl group; a second silicone resin component including at least one of a second silicone resin A represented by formula (51A) shown below and a second silicone resin B represented by formula (51B) shown below, the second silicone resin A containing an aryl group and a hydrogen atom directly bound to a silicon atom, the second silicone resin B containing an aryl group and a hydrogen atom directly bound to a silicon atom; and a catalyst for hydrosilylation reaction.