The cleanliness test is suitable for the inspection of surface contamination, which is invisible to the naked eye. This test enables us to evaluate the quality and the quantity of the contaminant particles, which are responsible for lots of breakdowns later in the life cycle of products. As my first task, I had started my work with familiarizing myself with the cleanliness test, which is performed in the Central laboratory of Continental Automotive Hungary, and the collection of influential parameters of the examination. Based on the parameters, I created the detailed model of the procedure, laying emphasis on the optical microscopic evaluation method, because my task was to analyze and optimize this process. I had reviewed every possible influential factor and then I chose five (brightness, magnification, mode of illumination, focus, binarization threshold) of them, which were examined henceforth. I analyzed the influence of all parameters on the results of the measurements. Based on this data, I came to the conclusion that the evaluation is mostly affected by the focus setting and the binarization threshold. Via further experiments, I was looking for the ideal settings of the two aforementioned parameters or the required algorithm. Next, I defined the important steps of the cleanliness test method in detail, and I made suggestions on the adequate usage of the adjustments. In the end, I have created a simple, easily feasible checking method to the optimized procedure. The heart of the matter is that we judge the quality of our procedure based on one repeatability and one reproducibility test. According to my analysis the cleanliness test could be characterized with 21 % reproducibility and 6 % repeatability error rate.