This study investigates the structural behavior of precast lightweight sandwich panels with dimensions of (500 × 500 mm) and 120 mm height. Specimens consists of three layers: concrete face wythes (with thicknesses of 45 mm and grades of (80, 70) MPa) and high-density foam (with thickness of 30 mm) as a core material. Steel and carbon fiber shear connectors (rods and strips) were used in panels with angles of (45°, 60° and 90°). Three-point flexure load test was carried out on all panels. Obtained results were studied with predicted ultimate loads from ANSYS software and the theoretical extremes capacities of 0% and full-composite cases to evaluate the effects of changing components. Strength/weight ratio and degree of composite action were obtained to can judge the panels with effective parameter. It was found that adding carbon fiber strips has a high positive effect in degree of composite action. Steel bars shear connectors were the optimum shear connectors' type with high strength concrete. Carbon fiber strips and rods shear connectors were the best shear connectors' type with light high strength concrete. All properties of specimens enhanced with the decrease of the angle of shear connectors with both of steel and carbon fiber shear connectors. Angle of 45° is the optimum angle that resists the flexure load, obtaining high degree of composite action and high strength/weight ratio. It also obtained the highest percent of predicted ultimate loads from ANSYS software. Keywords Precast concrete sandwich panel • Lightweight units • Shear connector • Carbon fiber • Lightweight concrete • Strength/weight • Composite • Shear flow Abbreviations FCR Carbon fiber rods with diameter of 12 mm FCS Carbon fiber strips with cross section of (50 mm) × (1.2 mm) HD foam High density foam HSC High strength concrete LHSC Light high strength concrete