Interest in the micro-injection molding (μIM) process has grown as the demand for micro parts increased for various electronics, transportation, communications, biomedical and other applications. Recently, we have conducted an intensive research program to understand the details of this process and the material-process-property relationships for various polymers. In the present study, a micro-gear micro part was presented, in order to investigate the effects of processing conditions on microstructure, mechanical properties, and thermal properties, microtomed and examined using polarized light microscopy, and differential scanning calorimetry for investigation of morphology. Various microstructural features, such as morphological layer thickness and crystalline polymorphs, were observed and analyzed in light of the thermomechanical history. A skin-core region was observed, with spherulites predominating the core region, and highly oriented lamellae appeared in the skin layer. Numerical simulation of filling phase of micro gear gives us a detailed description of the thermal history and flow, in which contribute to better understanding on the origins differences in the morphologies among the layers across the part thicknesses in view of the prevailing process conditions. Keywords: Micro injection, flow behaviours, crystalline, polymer melt, numerical.