Miniaturisation of common laboratory techniques has gathered significant interest in the last few decades with both academic and industrial researchers seeking to reduce waste, sample volume, and limits of detection for a wide range of applications. These goals present a unique challenge that originally spurred the creation of the multidisciplinary field of microfluidics in the 1980s. In the same time-frame 3D printing has progressed from its inception by Charles Hull in 1983 and developed into a common industry technique used at the design and prototyping stage of product development. 3D printing is now also used in custom end-user products in automotive, aerospace, and biomedical industries. Despite this, achieving internal features and voids at the micro-scale via 3D printing remains a major challenge. In this thesis, Mask Projection micro-Stereolithography (MPμSL) was used as a fabrication method for the production of microscale internal voids and features toward achieving an ultra-rapid prototyping method for microfluidic applications. MPμSL is an ideal replication method for microfluidic applications as the working material is a liquid photo-polymer resin and thus can be removed from internal structures with relative ease. In addition, unlike classical multi-step fabrication methods that are prone to delamination, MPμSL enables the production of micro-scale capillaries capable of withstanding higher pressures in a single step. MPμSL build quality, channel reproducibility, channel size and channel shape were examined, and process limitations were characterised. The so-called ‘overcuring’ of the liquid polymer resin presents the main obstacle in the creation of microscale channels and features using this technique and hence was a primary focus of this thesis. Material characterisation techniques used to determine the nature of the photopolymer materials were applied and a mathematical model was developed and applied to predict areas where overcuring is likely to occur. This model forms the basis of the novel design algorithm developed in this thesis to mitigate for the overcuring effect. Finally, the new algorithm was applied to the production of internal features. The resulting increased control over microchannel dimensions and improvement in repeatability of the technique was quantified.