We investigate chaotic synchronization in the generalized sense in unidirectionally coupled erbium-doped fibredual-ring lasers. Numerical simulation shows that no matter whether the two different erbium-doped fibre dual-ringlasers are chaotic or not before coupling, they show generalized synchronization with a suitable unidirectional couplingcoefficient under which the maximum condition Lyapunov exponent is negative. We also use the auxiliary systemapproach to detect the generalized synchronization.