A curable organopolysiloxane composition can be used as a sealant or a bonding agent for optical semiconductor elements. The composition comprises at least the following components: (A) a multi-constituent, alkenyl-containing organopolysiloxane; (B) an organopolysiloxane that contains silicon-bonded hydrogen atoms and comprises constituent (B-1) containing at least 0.5 wt. % of silicon-bonded hydrogen atoms and constituent (B-2) containing at least 0.5 wt. % of silicon-bonded hydrogen atoms, and, if necessary, constituent (B-3), an organopolysiloxane; and (C) a hydrosilylation-reaction catalyst. The composition can form a cured body that possesses long-lasting properties of light transmittance and bondability, and relatively high hardness.