A roller curtain fixing bracket assembly includes a left support, a right support, a decoration board and two cover boards covering the left and right supports. A roller curtain device can be installed between the main bodies of the left and right supports. Each of the left and right supports has a plane board main body and several fixing boards protruding from outer edges of the plane board main body. Front edge of each of two fixing boards extending from two sides of the plane board main body is formed with a split. The decoration board has a horizontal panel and a vertical panel. A top end and a certain section of the vertical panel are formed with hook bars inserted and latched in the splits of the left and right supports and assembled therewith. The cover boards serve to conceal the seams between the supports and the decoration board.