In recent years, ceramic particles reinforced magnesium based composites have been considered in many researches because of their high specific strength and low density. Non-reactive in-situ process is one of the newly emerged method, in which of recycling of its scraps are advantageous. In the present work, the Mg/Mg 2 Si composite was synthesize using non-reactive in-situ method. Thermal and chemical methods were utilized for modification of primary Mg 2 Si particles. A directional solidification system was fabricated for studying of solidification process and effect of cooling rate on reinforcement structure. The results showed that the produced composite was containing primary Mg 2 Si particles, Mg-Mg 2 Si eutectic structure and Mg matrix. Mechanical properties were reduced because of coarse and denderitic structure of primary Mg 2 Si particles. With increasing cooling rates, the Mg 2 Si precipitated polygonally while in lower cooling rates, it solidified dendritically, mechanical properties was increased in high cooling rates. On the other hand, with addition of 0.5 wt. % bismuth to the melt, the primary of Mg 2 Si particles were convert to polygonal structures and the average size of their particle were reduced. Tensile tests in three different temperature (24°C, 150°C and 220°C) applied to pure magnesium, non-modified composite and modified composite. Tensile properties of modified composite in 24°C and 150°C were increased in comparison with non-modified composite. Unexpected reduction of tensile strength was observed at 220°C. Keywords: Mg/Mg 2 Si composite, Non-reactive in-situ composite, Directional solidification, Cooling rate, Structure, Mechanical properties, Modification.