The huge requirement of aggregates for production of concrete and scarcity of natural aggregates in India calls for an urgent need to explore alternative source of sustainable aggregates. One of the possible source of alternate aggregate can be sintered flyash lightweight aggregate mainly produced using flyash generated as waste from thermal power plants through sintering process. In the present investigation, stressstrain behavior and modulus of elasticity (MOE) for structural lightweight concrete which is a basic property for conducting the linear and non-linear analysis of structural members has been investigated. The accurate determination of stress-strain and MOE of structural lightweight concrete is essential in order to determine maximum allowable deflections, stiffness, story drift for tall buildings, etc. To evaluate MOE, the cylindrical specimens of 150 mm diameter and 300 mm height have been subjected to uniaxial compression under strain controlled mode. The paper highlights the impact of measurement techniques in determining MOE of lightweight concrete made using sintered flyash lightweight coarse aggregate for wide range of w/b from 0.3 to 0.7. The three measurement techniques i.e. (a) Compressometer and Extensometer (b) Linear Variable Displacement Transducer (LVDT) have been adopted for MOE determination. The paper discusses gauge length impact (ratio of length measured along height to specimen height) on the stress vs strain plot of structural lightweight concrete wherein comparison of stress vs strain plots attained from LVDT (gauge length =300 mm) and compressometer/extensometer (gauge length =150/200 mm) has been analyzed. Both measurement techniques for determining MOE have been compared in line with procedure of IS: 516 (Part8/Sec1) (2021)[13] and ASTM C-469 (2014)[14] procedures. The stress strain behavior on which MOE of concrete depends has also been compared for both structural lightweight concrete and normal concrete. The difference between ratio of ultimate strain to strain at peak stress for lightweight concrete and normal weight concrete with increase in strength decreases significantly indicating the lightweight concrete is more brittle as compared to normal weight concrete. The stress strain curve of unconfined lightweight concrete indicates linear behavior upto 70-80 % of peak load as compared to normal weight concrete which gives linear behavior upto 35-50 % of peak load