A fixing assembly for carrying a bike includes a main body having a transverse hole provided therein with transverse ribs to be secured with a rod of a carrying stand on a motor vehicle. The main body is formed with a concave portion with vertical ribs for positioning a bike frame rod or a bike wheel thereon, having a first strap with lots of one-way ratchets and a second strap for receiving an engaging device that has a base to be secured with the second strap. The base is provided with a micro-adjusting member for adjusting combined tightness of the first and the second strap, and an engaging member for engaging the one-way ratchets of the first strap to prevent the first strap from moving reversely and a releasing member for pulling open the engaging member to release and separate the first strap and the second strap.