The aim of this work is to show theoretically the specificity of usury respect to the bank loan contracts. We prove that, in order to finance an investment project in a legal environment characterised by insufficient enforcement of property rights and asymmetric information, the usury lender can be more efficient than the legal one. Usury can be cheaper than the bank loan contract because in the usury contract the debt renegotiations are more likely to be implemented, given specific features of the usurer technology and a entrepreneur's decreasing risk aversion. We also show that an high level of interest rate do not represent a necessary nor a sufficient condition for the existence of usury contracts. Therefore the Italian Law Against Usury, based on the assumption that sufficient high interest rates are likely to be linked with usury agreements, is absolutely inconsistent with the above economic approach.