This article focus to Define and Discuss on Adversary Justice System. The simplest way to discover the truth, based on the adversary model of prison justice, is by having an advocate to the prosecution and for the defense. Each advocate has the obligation for presenting the details from a partisan point of view. This system is meant to maximize the chances that all the relevant facts and arguments will likely be placed before a fact‐finder. Here briefly explain on the attorney-client privilege in a criminal case, Defense counsel justification for representing a guilty defendant and Functions of the defense lawyer.