In this work, the rheological characterization of the gel point in polymer-modified asphalts is carried out. The viscoelastic properties of polymer-modified asphalts, in which the polymer is styrene-ethylene butylene-styrene (SEBS) with grafted maleic anhydride (MAH), were measured as a function of MAH concentration. The crosslinking reaction that leads to gelation is characterized by power-law frequency-dependent loss and storage modulus (G '' and G '). The relaxation exponent n (a viscoelastic parameter related to the cluster size of the gel) and gel strength S (related to the mobility on the crosslinked chain segments) were determined. The value of the power-law exponents depends on the composition of polymer, ranging from 0.30 to 0.56, while the value of the rigidity modulus at the gelation point (S) increases with the amount of reactive groups of the modifier polymer. Both n and S are temperature-dependent in the blends. The blends containing gels present a coarse morphology, which is related to the rheological properties of the matrix and dispersed phase. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2422-2430, 2011