Blob is a basic form in the gray-scale image, and has important application in image analysis. In this paper, a novel blob form filter (BFF) is proposed to detect the blob target in image. Based on the principle of percentile filtering, the BFF has strong robustness to noise. The experimental results show that BFF cannot only effectively detect the blob region specified size from binary image and gray-scale image with noise, but can also get the blob form very close to the original form.