We determine the exact values of the linear complexity of 2pperiodic quaternary sequences over Z 4 (the residue class ring modulo 4) defined from the generalized cyclotomic classes modulo 2p in terms of the theory of of Galois rings of characteristic 4, where p is an odd prime. Compared to the case of quaternary sequences over the finite field of order 4, it is more difficult and complicated to consider the roots of polynomials in Z 4 [X] due to the zero divisors in Z 4 and hence brings some interesting twists. We prove the main results as follows Linear Complexity =