Objectives: This research is seeking to answer a basic question: "Have three five years Socio-Economic plans in first, second, third economic development could create poverty changes in Semnan province or not (1368 - 83 )? Doing so, poverty line and the poverty indices are estimated concerning urban and rural areas during 1st (1989-1993), 2nd (1995-1999) and 3rd (2000-2004) plans. Method: In order to estimate poverty line and the poverty indices, the expenditure-income data, price indices concerning urban and rural areas during three socio-economic plans (1989-2004) is used. Consumer behavior is analyzed by dividing the total urban and rural consumption into 8 main commodity groups: the food and beverage, clothing, housing, housing furniture’s and services, health and medical cares, transport and communications, entertainment and educations, and other commodities. Then, households poverty line, and Head-Count, Poverty Gap and Foster, Greer, Thorbecke index have been found based on household survey data using the Liner Expenditure System (LES) of equations with iterative seemingly unrelated Regression (ISUR) method corresponding to rural and urban areas of Semnan province. Finding: Poverty lines in urban and rural areas during the three socio-economic plans have had upward trends in urban areas, it has increased by more than 17 times and has reached from 1042791 Rials at the first year of the 1st plan to 17761513 Rials at the end of the 3rd plan. In rural areas, the poverty line was 691931 Rials at the first year of the 1st plan which by 18 times increase has reached to 12409611 Rials at the end of the 3rd plan. Results: One of the main reasons of the increase has been the high inflation rate. Although, the poverty lines in urban areas have always been higher than that in the rural areas, the rural Head count poverty has been more than urban, but the poverty gap and FGT index in urban have been more than those in rural areas. All poverty indices have increased during the 1st development plan and reduced during the 2nd and 3rd plans.