The proton-ligand and metal-ligand stability constants of the complexes of Cu(II), Ni(II),Co(II) with 1-Benzothiazol- 2-yl-3-(2-hydroxy phenyl)-5-(4-methoxy phenyl) pyrazoline (L1), 1-Benzothiazol-2-yl-3-(2-hydroxy phenyl)-5-phenyl pyrazoline (L2), 1-Benzothiazol-2-yl-3-(2-hydroxy phenyl)-5-(4-chloro phenyl) pyrazoline(L3), 1-Benzothiazol-2-yl- 3-(2-hydroxy-5-methyl phenyl)-5-(4-methoxy phenyl) pyrazoline (L4), 1-Benzothiazol-2-yl-3-(2-hydroxy-5-methyl phenyl)-5-(4-chloro phenyl) pyrazoline(L5) and 1-Benzothiazol-2-yl-3-(2-hydroxy-5-methyl phenyl)-5-phenyl pyrazoline(L6) have been determined by pH-metric method in medium of 80% acetone-water mixture at 0.1M ionic strength and at (30± 0.1)0C temperature