On the basis of transient network theory, we study linear viscoelasticity of physical gels formed by polymers that carry two different species of associative groups. The simplest but an important case, discussed in this paper, treats linear chains carrying two A functional groups at both ends and one B group at the center of the chain. It turns out that the complex modulus is described by the two-mode Maxwell model when condition beta(A) much greater than beta(B) or beta(A) much less than beta(B) holds, where beta(i) (i = A,B) is the detaching rate of an i associative group from the junction. In the latter case, two rubbery plateaus appear in the storage modulus, and structural transformations from a network of A backbone to that of connected B micelles are expected to occur at characteristic frequency of omega similar or equal to beta(A) + beta(B). (C) 2004 The Society of Rheolog.