To study the mechanism and kinetics of the decomposition of NaBH4 in an electroless nickel bath, we investigate the effects of concentration of NiCl2, concentration of NH4Cl, pH, temperature, and amount of Ni powder on the rate of decomposition of NaBH4. The results indicate that the decomposition of NaBH4 is accelerated by H+ ions and Ni2+ ions. The kinetic orders of H+ and Ni2+ in the NiCl2/Na2C4H4O6 system are 0.4 and 1, respectively, but the kinetic order of H+ is 0.56 in the NiCl2/Na2C4H4O6 + NH4Cl system. The rate of decomposition decreased with addition of NH4Cl. The results show that the rate of decomposition of NaBH4 is accelerated by the presence of nickel powder in the bath. The experimental results and theoretical predictions of the model developed from the proposed mechanism are consistent. The kinetic equation for decomposition of NaBH4 in electroless Ni bath is expressed as [(1/v)(dN(H2)/dt)]o = 4(k1W(Ni,0) + k2C(H+,0a1))C(BH4-,0) + 2(k6W(Ni,0) + k7C(H+,011))C(BH4-,0)C(Ni2+,0) in which k1, k2, k6, and k7 are 32.25 g-1 min-1, 2.49 X 10(5) M-1 min-1, 2.43 X 10(3) g-1 M-1 min-1, and 5.63 X 10(6) M-2 min-1, respectively. al is 0.4 for the NaBH4 system and NiCl2/Na2C4H4O6 system and 0.56 for the NiCI2/Na2C4H4O6 + NH4Cl system.