The proton-ligand stability constants of five important substituted 5-(2-hydroxy phenyl) pyrazoles and metal-ligand stability constants of their complexes with Co (II) and Ni (II) metal ions have been determined in 70% v/v dioxane-water media at different ionic strength (0.02, 0.04, 0.06, 0.08, 0.1 mol dm-3 of electrolyte, KNO3) and at constant temperature of 303.15K by potentiometric method. The pK and logK values decreased with increase in ionic strength of medium, which indicated the opposite charges on reacting species. The values of stability constants for Ni (II) were greater than for Co (II) metal ion. The thermodynamic stability constants at zero ionic strength have also been determined. The effect of presence of an extra electrolyte on dissociation and complex equilibria of pyrazoles has been studied.