A curable organopolysiloxane composition that can be used as a sealant or a bonding agent for optical semiconductor elements and comprises at least the following components: (A) an alkenyl-containing organopolysiloxane that comprises constituent (A-1) of an average compositional formula and constituent (A-2) of an average compositional formula; (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 represented by an average molecular formula, constituent (B-2) containing at least 0.5 wt. % of silicon-bonded hydrogen atoms and represented by an average compositional formula, and, if necessary, constituent (B-3) of an average molecular formula; 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 low hardness.