THE ACCURATE DETERMINATION OF acidity AND STABILITY constants VALUES ARE FUNDAMENTAL TO UNDERSTANDING THE BEHAVIOR OF LIGANDS AND THEIR INTERACTION WITH METAL IONS IN AQUEOUS SOLUTION. SUCH AN UNDERSTANDING IS IMPORTANT IN A WIDE VARIETY OF AREAS, SUCH AS METAL IONS IN BIOLOGY, IN BIOMEDICAL APPLICATIONS, METAL IONS IN THE ENVIRONMENT, EXTRACTION METALLURGY, FOOD CHEMISTRY AND METAL IONS IN MANY INDUSTRIAL PROCESSES. VARIOUS METHODS FOR THE DETERMINATION OF DISSOCIATION constants, SUCH AS POTENTIOMETRIC, SPECTROPHOTOMETRIC, CONDUCTOMETRIC, AND SPECTROSCOPIC METHODS, HAVE BEEN REPORTED.SPECTROPHOTOMETRIC METHOD IS APPLICABLE TO THE COMPOUNDS WHOSE CONCENTRATIONS OR EXTINCTION COEFFICIENTS ARE NOT DETERMINED. IT PROVIDES MORE EXACT DISSOCIATION constants THAN OTHER METHODS, EVEN FOR POLYPROTIC COMPOUNDS WITH ALMOST EQUAL PKA, VALUES AND COMPOUNDS WITH EXTREMELY ACIDIC OR EXTREMELY BASIC PROPERTIES. THE MOST WIDELY USED PROGRAMS AND ALGORITHMS FOR THE DETERMINATION OF acidity constants FROM SPECTROPHOTOMETRIC DATA ARE SQUAD, SPECFIT, DATAN AND KINFIT.IN THIS INVESTIGATION, SPECTROPHOTOMETRIC DATA WAS USED FOR THE DETERMINATION OF DISSOCIATION constants OF SOME DYES INCLUDING EOSIN Y, FAST GREEN FCF, 4- (2-PYRIDYLAZO) RESORCINOL (PAR) AND AMINO HYDROXY NAPHTHALENESULFINIC ACID IN AQUEOUS SOLUTION BY MEANS OF HYPSPEC PROGRAM AS A NEW VERSION OF PHAB PROGRAM. ALSO THE DISTRIBUTION DIAGRAMS WERE DEPICTED BY HYSS2009. THE OBTAINED RESULTS SHOW THE GOOD AGREEMENT WITH THOSE FROM LITERATURE.