Two multidentate ligands: N,N'-di-(propionic acid-2'-yl-)-2,9-di-aminomethylphenanthroline (L1) and N,N'-di-(3'-methylbutyric acid-2'-yl-)2,9-di-aminomethylphenantliroline (L2) were synthesized. The hydrolytic kinetics of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) catalyzed by complexes of L1 and L2 with La(III), Gd(III) have been studied. Both LnL and LnLH(-1) have been examined as catalysis for the hydrolysis of HPNP in aqueous solution at 298 K, I = 0.10 mol dm(-3) KNO3 at pH range 7.4-9.1, respectively. Kinetic studies show that both LnL and LnLH(-1) have activity, but LnLH(-1) is more active than LnL in the hydrolysis reaction of HPNP. The second-order rate constants of hydrolysis of HPNP are k(GdL1H-1) = 0.0466 mol(-1) dm(3) s(-1), k(GdL1) = 0.000037 mol(-1) dm(3) s(-1) for GdL1H(-1) and GdL1, respectively. New mechanism was proposed for the hydrolysis reaction of HPNP catalyzed by LnL and LnLH(-1). (c) 2006 Elsevier B.V. All rights reserved.