The present invention relates to a seat adjusting mechanism for vehicle comprising a seat cushion frame which has at a lower part thereof a latch assembly being locked or unlocked to a locking pin of a vehicle part, a connecting plate which is fixedly coupled to an end part of the seat cushion frame and a seatback frame which is rotatably coupled to an end part of the connecting plate through a recliner, further comprising a driving link which is rotatably coupled to the connecting plate and is rotated in connection with the seatback frame when the seatback frame is rotated; a pre-latch link which is rotatably coupled to the connecting plate apart from the driving link and which, when the driving link is rotated over a predetermined angle, is rotated together to a predetermined extent in contact with the driving link; and a latch link which is rotatably coupled to the connecting plate with the same rotating axis as the pre-latch link and has an end part coupled to a cable end part for an operation of unlocking the latch assembly, and which is contacted, pressed and rotated by the pre-latch link from a predetermined position within the predetermined extent where the pre-latch link is rotated, thus unlocking the latch assembly through the cable end part. According to the present invention, the seat can be folded and erected by just a simple operation if required.