A pull cord control device for Venetian blind includes a mounting body made up of an engagement piece having symmetrical registration posts for positioning rollers to be mounted thereto, and a limiting piece equipped with a pair of teeth racks symmetrically extending at both sides thereon in mesh with a control gear disposed at one side thereof to define a confinement space there-between for a coupling post with an embossed mounted thereto to be located in the middle thereof. A U-shaped groove is vertically indented at the inner side of the limiting piece therein for a U-shaped and metallic protection rod to be located therein and abutted against the upper edge of the confinement space thereof A decoration lid of an oval shape with a pull-cord passage slot disposed thereon is integrally formed at one end of the limiting piece thereof with the protection rod exposed precisely at the inner lower edge of the pull-cord passage slot thereof. A cover having coupling holes to be registered with the limiting body thereof is provided with a plane abutting facet to be precisely abutted against the inner upper edge of the decoration lid thereby. Thus, a pull cord guided through the upper edge of the protection rod before suspended downwards through the pull-cord passage slot of the decoration lid is refrained from directly rubbing against the frame edges of the pull-cord passage slot when drawn to any sides therein to fold/unfold the Venetian blind thereof, facilitating a smooth operation of the pull cord to achieve the best using condition thereof.