Although the Convention on the Rights of the Child (CRC), which was ratified by the Iranian parliament in March 1994, had a paramount role in considering children’s interests, the notion of the Best Interest of the Child (BIC) was not entered in the Iranian legal system by then. BIC is more recognized in the Imamiah jurisprudence which is the base of the legal system, as Ghebta which is a golden key in the decisions concern to the children. It seems that joining the convention and assigning Article 3 to the best interest of the child has promoted its usage and applications in the law and the precedent. Principle 21 of the Constitution, Articles 1041, 1169, 1184 of Civil Code, Articles 88, 354 of Islamic Penal Code and Articles 29, 41, 42, 43, 45 Family Protection Act are notable samples of this application. Besides, Family judges nowadays take decisions based on BIC more than before. However, the ambiguity of the BIC and diversity of the interpretations used by the courts have made malfunctions in the system and in some occasions have led to contradictory decisions in the same situations. Here, in the first step, we are going to clear the BIC by reviewing Islamic scholar’s views and determining the criteria by considering it in the growth levels. The second step will be BIC status in the Iranian Legal system and the precedent. This study showed that the fluidity of the BIC should not cause insufficiency and at least we need general criteria based on the growth levels.