Property testing is a rapid growing field in theoretical computer science. It considers the following task: given a function f over a domain D, a property ℘ and a parameter 0<ε<1, by examining function values of f over o(|D|) elements in D, determine whether f satisfies ℘ or differs from any one which satisfies ℘ in at least ε|D| elements. An algorithm that fulfills this task is called a property tester. We focus on tree-likeness of quartet topologies, which is a combinatorial property originating from evolutionary tree construction. The input function is f Q , which assigns one of the three possible topologies for every quartet over an n-taxon set S. We say that f Q satisfies tree-likeness if there exists an evolutionary tree T whose induced quartet topologies coincide with f Q . In this paper, we prove the existence of a set of quartet topologies of error number at least c(n4) for some constant c>0, and present the first property tester for tree-likeness of quartet topologies. Our property tester makes at most O(n 3/ε) queries, and is of one-sided error and non-adaptive.