In this paper, a novel method for off-line handwritten signature verification is presented. The method relies on ink concentration of a handwritten signature. The ink concentration is obtained by combining surface desorption atmospheric pressure chemical ionization mass spectrometry (SDAPCI-MS) and the Similarity Algorithm. The image of the signature is obtained by analyzing the ions of the mass spectra and extracts the relative more ink concentration as the feature. Firstly, the Euclidean distance is calculated among the handwritten signatures, but the result is not satisfied. At the end, using Similarity Algorithm, signatures is classified as authentic or forged one. The results demonstrate that this method is simple and rapid for verification of handwritten signatures.