Abstract. This paper investigates the use of tree automata with global equalities and disequalities (TAGED for short) in reachability analysis over term rewriting systems (TRSs). The reachability problem being in general undecidable on non terminating TRSs, we provide TAGEDbased construction, and then design approximation-based semi-decision procedures to model-check useful temporal patterns on in nite state rewriting graphs. To show that the above TAGED-based construction can be e ectively carried out, complexity analysis for rewriting TAGEDde nable languages is given. Recently, reachability analysis turned out to be a very e cient veri cation technique for proving properties on in nite systems modeled by term rewriting systems (TRSs for short). In the rewriting theory, the reachability problem is the following: given a TRS R and two terms s and t, can we decide whether s → * R t or not? This problem, which can easily be solved on strongly terminating TRSs, is undecidable on non terminating TRSs. However, on the one hand, there exist several syntactic classes of TRSs for which this problem becomes decidable [16,20,34]. On the other hand, in addition to classical proof tools of rewriting, given a set E ⊆ T (F) of initial terms, provided that s ∈ E, one can prove s → * R t by using over-approximations of R * (E) [21,16] and proving that t does not belong to these approximations. Recently, the veri cation of temporal properties of systems modeled by TRSs has been investigated [15,28,27]. To apply these very interesting and promising theoretical results to applications This work has been funded by the French ANR-06-SETI-014 RAVAJ project.