Glass reinforced plastic (GRP) structural members are currently being produced successfully by pultrusion and are used in an increasing number of civil engineering applications. Measurement of the mechanical properties of the composite material is necessary for numerical structural analysis and design. The mechanical properties of composite materials are determined by specific coupon test methods or by analytical models (giving estimated linear elastic properties). However, the experimental test method may not economical or practical for the determination of mechanical properties of pultruded GRP structural sections. The elastic properties of the pultruded GBP box section have been estimated using micro-mechanical models and classical lamination theory. ASTM D3039 specimens have keen ased to provide the experimental longitudinal tensile properties of pultruded GRP box section to verify the analytical method.