Several systems have been proposed for generating persuasion dialogs in which agents try to persuade each others to change their mind on a state of affairs. In this paper, we focus on the evaluation of the quality of those dialogs. We particularly propose three families of measures: i) measures of the quality of exchanged arguments, ii) measures of the behavior of each participating agent in terms of coherence, aggressiveness and the novelty of her arguments, iii) measures of the quality of the dialog itself in terms of relevance and usefulness of its moves. A notion of conciseness of a dialog is also introduced. For each persuasion dialog, we compute its ideal dialog which is a concise sub-dialog. The closer a dialog to its ideal sub-dialog, the better it is.