One of the most important biological material that plays a vital role in living systems is peptides which participate in neural tissues and the structure of lipids and hormones. Hence, the identification of them is important due to determining their biological role. Mass Spectrometry is a known method with high speed and sensitivity to recognize these kinds of materials. As regards, the ion attachment mass spectrometry (IAMS) technique usually reduce the sample fragmentation and the [cation-sample]+ can be detected as a distinct signal, the identification of some dipeptides has been studied by this method in the gas phase. The alkali salts including NaF, NaOH, and LiCl, were used to provide cations in the laser desorption ionization process (LDI). Differences between the fragmentation patterns of the four dipeptides consisting phenylalanilalanine (Phe-Ala), tyrosiylalanine (Tyr-Ala), phenylalanylphenylalanine (Phe-Phe), and Alanylglutamine (Ala-Gln) in the presence and absence of obtained cations from sodium fluoride, sodium hydroxide, and lithium chloride were investigated. The assignment of peaks related to these dipeptides in the absence of cations showed that the Phe-Ala and Phe-Phe were completely decomposed and the highest mass has been observed at 120.0 m/z which correspond to the [C 6 H 5 CH 2 CHNH 2 ] + . On the other hand, the attachment of the sodium ions which are naturally in the materials, to the Tyr-Ala and Ala-Gln dipeptides caused to appear [(Tyr-Ala) Na] + and [(Ala-Gln)-H+2Na] + peaks, respectively. The mass spectra of different dipeptides in the presence of cations have shown diverse behaviors. The Phe-Ala in the presence of difference salts has shown a similar pattern so that with NaF and NaOH the peak related to [(Phe-Ala)-H+2Na] + and with LiCl the peak correspond to [(Phe-Ala)-H+2Li] + were appeared. In the mass spectrum of Tyr-Ala with addition NaF, the base peaks were observed with [(Tyr-Ala)+Na] + and [(Tyr-Ala)-H+2Na] + structures. But, in the presence of NaOH and LiCl, the base pick has not appeared. The [Phe+2Na] + ion with other smaller fragments of Phe-Phe in the presence of NaF and NaOH were observed which indicated that the peptide bond of Phe-Phe in the presence of salts has weakened and broken completely down in the gas phase. The similar behavior was observed in the presence of LiCl which the peak related to [Phe+2Li] + ion has appeared. Moreover, no base peak was observed for the Ala-Gln in the presence of these cations and only a dimer structure, [2(Ala-Gln)-NH2] + , was observed in the presence of NaOH. It should be noted that for all dipeptides in the presence of LiCl, lithium salt clusters were observed with chlorine isotopes. Finally, in order to identify the appropriate positions of sodium ions in the structures of dipeptides in the IAMS procedure, the calculations of the density functional theory (DFT) were used and the most stable structure of the sodium-dipeptides was detected.