A slat angle adjustment mechanism for Venetian blind includes a body shell and a transmission unit including a transmission gear set and retractable member. The transmission gear set includes a gear having a position-limiting hole corresponding a second through hole of the body shell, and a screw rod with an extension shank. The retractable member is connected to and movable back and forth along the extension shank of the screw rod. When pulling the retractable member, the retractable member is moved along the extension shank of the screw rod from a first position; when pushing the retractable member, the retractable member is moved along the extension shank of the screw rod from the second position back to the first position. Thus, subject to the retractable characteristic, the slat angle adjustment mechanism prevents damage during packaging.