We show that the uniform termination problem is undecidable for length-preserving semi-Thue systems having 9 rules. We then give an explicit uniformly terminating semi-Thue system having 9 rules which is “universal with respect to termination problems” in some sense. It follows that there exists a fixed rule (u0, v0) such that ∪ {(u0, v0)} has 10 rules and undecidable termination problem.