An apparatus and method are described for down-converting from a source operand to a destination operand with masking. For example, a method according to one embodiment includes the following operations: reading a source operand value to be down-converted from a first value to a down-converted value and stored in a destination location; reading each mask register bit stored in a mask register, the mask register bit(s) indicating whether to perform a masking operation or a conversion operation on the source operand value; if the mask register bit(s) indicates that a masking operation is to be performed, then performing a specified masking operation and storing the results of the masking operation in the destination location; and if the mask register bit(s) indicates that a masking operation is not to be performed, then down-converting the source operand value and storing the down-converted value in the specified destination location.