In order to establish the evaluation on uncertainty of plate counting results on colonies count in fermented Lepidium sativum.,the source of evaluation on uncertainty of plate counting results on colonies count in fermented Lepidium sativum was analyzed according to the the "Guidelines for the Evaluation of Incertainty in Food Microbiology Measurement" and the "Evaluation and Expression of Incertainty Determination". The synthetic uncertainty and extended uncertainty were evaluated. The results showed that the proportion order of the components of the uncertainty introduced during the total number of colonies plate counting was: repeatability test ＞ dilution ＞ sampling ＞preparation sample ＞ ambient temperature. The extension uncertainty of the total number of colonies was 218 CFU/g,and the value range was 5 782-6 218 CFU/g,including the factor k=2. This method was suitable for evaluating the uncertainty of the total number of colony plate counting under similar conditions.