In this paper, a method of automatic inspection of silk spinning yarn fineness through image processing was developed. The acquired images were processed by image processing methods. Three thresholding methods were used and compared. The diameter and its CV value were obtained by processing the binary images. The results obtained were compared with measurements performed by means of EIB (Electronic Inspection Board). Yarn fineness and its CV value were obtained and the experimental results prove that the iterative method is more suitable for thresholding images to measure the silk yarn fineness.