According to recent advancements in additive manufacturing (AM) technology, also known as 3d printing, the role of AM has changed from the conventional rapid prototyping (RP) to direct fabrication of functional parts. The AM technology based on layer-by-layer manufacturing has a limitation in its poor surface finish and mechanical strength, especially along the thickness direction. This study proposes a new post-processing method for thermoplastic AM products with the goal of improving surface finish and mechanical strength. The proposed method, called constrained remelting, uses a metal mould with a negative shape that surrounds the printed polymer part. This mould is heated near the melting temperature of the polymer material so that the printed sample is melted and reshaped inside the mould. To evaluate changes in surface finish and mechanical strength, tensile specimens were printed and tested with various build directions; the tensile test revealed that the Z-directionally printed specimen had much lower mechanical strength than the specimens built along X- or Y- directions. Remelting experiments were then performed for the Z-directionally printed specimen under various remelting conditions (remelting temperature and initial thickness), and the resulting changes in surface finish and tensile strength were investigated. Among these remelting conditions, the 160°C remelting temperature and 4.0 mm thickness condition provided the best result where surface finish and tensile strength were improved significantly so as to be comparable to those of injection-moulded products.