The study focuses on developing a poly(lactic acid) (PLA) composites with 58S bioglass microspheres (58S BG) for improving the mechanical properties of bone tissue engineering scaffolds by injection molding process. The collaboratory research institution, Leibniz Institute of Polymer Research Dresden (IPF), provides a design of new-type microinjection molded tensile rod with and without weld line which can be used to observe the micro features of mechanical properties on PLA composites. The influences of injection molding parameters have been optimized for the mechanical properties according to design of experiment (DoE) with varying injection velocity, melt temperature, and packing pressure. The mechanical behavior of sample with and without weld line have been improved by lowering the melt temperature to obtain in a thicker skin layer. The Young’s modulus of an injected samples increased from 13.7 GPa to 14.0 GPa for adding 5-10wt% 58S BG powder in PLA matrix. However, the tensile strength and elongation at fracture of samples are rapidly falling and convert it to brittle behavior due to the lower bonding properties between polymer and inorganic particle reinforced material bioglass. Thus, considering the balance of mechanical properties, it is estimated that 3.9wt% BG content is the best mixing ratio.