A new image analysis methodology for automatic sizing of oxalate crystals was developed using optical micrographs. Assuming a rectangular projected shape of oxalate crystals, the algorithm was tested to ensure that statistically meaningful results for the crystal size distributions of different crystal populations were generated. Images of oxalate crystals were collected using a Nikon inverted optical microscope with an automated motorised stage. The algorithm for automatic image analysis, developed in a Matlab computational environment, generates a 2-D crystal size distribution, with the crystal length and width as coordinates. Reproducibility of the results from the newly developed image analysis technique was tested by processing a number of laboratory prepared oxalate samples. The results were found to be dependent on the filtering procedures applied to remove overlapping crystals, as well as, on the number of crystals taken into account in the image analysis step. For the purpose of presentation, the 2-D crystal size distributions generated by the image analysis algorithm were converted to 1-D equivalent diameter crystal size distributions. The 1-D crystal size distribution can be easily validated against results obtained by other commercially available particle sizing devices.