Disclosed is a system of determining an outlier of a lease case for estimating a real estate lease price comprising : a real estate information database in which attribute information and price information of each real estate are stored in advance for a plurality of real estate; a target real estate input module which receives transaction information including a lease price of a target real estate desired to determine an outlier of a lease case; a similar real estate search/collection module which searches and collects a nearby similar real estate from the real estate information database based on an address and the transaction information of the target real estate inputted in the target real estate input module; and a lease price outlier determination module which selects an optimal lease price estimation model by using the lease price from the price information of similar real estate collected in the similar real estate search/collection module, calculates a lease price estimation value of the target real estate by the selected lease price estimation model, and compares the lease price of the target real estate inputted in the target real estate input module with the lease price estimation value estimated by the lease price estimation model so as to calculate and determine a lease price outlier of the target real estate.