Anatoxin–a(S) "Salivary"[a] is a naturally occurring cyanotoxin commonly isolated from cyanobacteria (specifically of the genus Anabaena) and causes excess salivation in mammals via inhibition of acetylcholinesterase. Anatoxin–a(S) is structurally a cyclic N–hydroxyguanine organophosphate with a phosphate ester moiety. Parameters such as FT–IR and Raman vibrational wavelengths and intensities for single crystal Anatoxin–a and Anatoxin–a(s) are calculated using density functional theory and were compared with empirical results. The investigation about vibrational spectrum of cycle dimers in crystal with carboxyl groups from each molecule of acid was shown that it leads to create Hydrogen bounds for adjacent molecules. The current study aimed to investigate the possibility of simulating the empirical values. Analysis of vibrational spectrum of Anatoxin–a and Anatoxin–a(s) is performed based on theoretical simulation and FT– IR empirical spectrum and Raman empirical spectrum using density functional theory in levels of F/6–31G*, HF/6– 31++G**, MP2/6–31G, MP2/6–31++G**, BLYP/6–31G, BLYP/6–31++G**, B3LYP/6–31G and B3LYP6–31–HEG**. Vibration modes of methylene, carboxyl acid and phenyl cycle are separately investigated. The obtained values confirm high accuracy and validity of results obtained from calculations.