The determination of value of an industrial property is important for assessing ad valorem tax, insurance, management, sales, etc. Unfortunately, in the majority of the situations, market evidences, which are the most reliable evidences of value, do not exist. Therefore, the objective of this study is to develop a procedure to aid in the estimation of the value of such industrial units or groups of properties;Normally, sum of the present worth of future after-tax-cash-flow (ATCF) is a good criterion for determining the value of a property. Unfortunately, the ATCF, which in valuation procedures is known as operation returns, usually decline with the passage of time. With this basic assumption of declining operation returns, a simple model known as the Y model was proposed to represent the actual decline of operation returns;In order to test the validity of the Y model, data were collected and analyzed using the modified Delta method. The modified Delta method assumes that the factors that are responsible for the decline in operation returns of either unit or group properties are the decreasing service intensity and the increasing repair and maintenance costs. Unfortunately, data on the above factors are sometimes hard to find, especially for group properties. These can, however, be replaced by similar factors, namely, the decreasing gross operating revenue and the increasing operating costs;Using the above method and model, values of industrial properties at different ages were determined. These values compared well with the actual market evidences verifying the validity of the proposed Y model and modified Delta method for valuation of similar unit or group industrial properties. Thus, a depreciation method within the present worth principle that systematically recognizes the declining operation returns over the lives of industrial properties was developed in this study.