Abstract: Measurement uncertainty is to describe the result of suspicious quantification. In order to decrease experimental error and increase the accuracy of total bacterial counting test,quantities of 20 bacterial colonies in aquatic feed were selected as samples, and the measurement uncertainty of them were tested with the method of uniting standard deviation of total samples. The results showed that the expand uncertainty was 0.12; and the value range was lgA±0.12 when expressed as the mean value of two measurements.