Free online translators are in fact statistical machine translators that create translator models using parallel corpora. Although it’s not a new subject and many works are reported on that in recent years, it still suffers from lots of shortcomings and has a long way ahead. While the literature on machine translators is vast, there are only a few that evaluate free online machine translators in specific terms like idioms. The aim of this paper is to evaluate and compare four free online translators in terms of translating English idioms (including idiomatic phrasal verbs) into Persian. To that end, ten chosen texts from the book “oxford word Skills: idioms and phrasal verbs” were translated by four online translators, www.bing.com, www.translate.google.com , www.freetranslation.com and www.targoman.com , and the obtained results were compared in a subjectively method based on Aryanpur English to Persian dictionary. Comparison of the results shows that www.targoman.com has a better performance in translating idioms from English to Persian and as a result, it can be the best choice if the aim is to do so.