The micro injection moulding (µIM) process for the production of micro rings in thermoplastic elastomers (TPE) was investigated and optimized. The objective was to minimize the formation of air entrapments and the depth of micro weld line created on the surface of the TPE micro moulded rings. The defects were investigated by both experiments and numerical simulations of the µIM process. The results obtained from the simulation software were verified by comparison with the actual moulded parts. It was found that the simulation was accurate in the prediction of air entrapments and weld line placement. The µIM processing parameters had a large influence on the weld line depth and the air entrapment. In particular, it was found that low settings of the injection speed and of the clamping force increased the air evacuation from the cavity, thus minimizing the weld line depth and the presence of air entrapment defects.