Relative attitude formation control systems are developed for multiple spacecraft, based on the line-of-sight measurements between spacecraft in formation. The proposed control systems are unique in the sense that they do not require constructing the full attitudes of spacecraft and comparing them to obtain the relative attitudes indirectly. Instead, the control inputs are directly expressed in terms of line-of-sight measurements to control relative attitude formation precisely and efficiently. It is shown that the zero equilibrium of the relative attitude tracking errors is almost globally asymptotically stable. The desirable properties are illustrated by numerical examples, including an image processing routine to simulate vision-based line-of-sight sensors.