According to existing literature in Islamic economics the implantation of the idea of Islamic banks emerged in the Egyptian countryside in 1963. Thereafter, this kind of institutions have spread all over the world to reach more than 700 banks operating in 60 countries with 38 million customers around the world with total assets of up to $2 trillion according to latest reports. However, the practices of these institutions have given rise to a very critical question: Are the existing Islamic banks practicing their transactions according to Islamic Shari'ah in substance rather than the forum? The objective of this study is to develop a specialized technical criterion to assess the extent to which Islamic banks adhere to the rules of the Islamic economics. Thus, the technical criterion was designed and then applied to a sample of Islamic banks in the Arab world. The study found that the percentage of banks that comply with the rules of the Islamic economics ranges between 29% and 90% of the Shari'ah standards. Therefore, the study recommends applying this test of Shari'ah standards on a regular basis to all Islamic banks to notify the Shari'ah boards of these banks with the results of the test, thus, paving the way for greater transparency of the customers of these banks.