It is well-known that hydrogen for portable applications can be generated by hydrolysis of sodium borohydride stabilized in an alkali medium over suitable catalysts. This paper describes hydrogen generation by hydrolysis of solid sodium borohydride (NaBH4) powder in a milli-scale semi-continuous reactor. Acidified (hydrochloric acid) water is used as an accelerator for hydrogen generation. The effects of liquid-solid interfacial contact area, NaBH4 loading, liquid flow rate, and temperature on the hydrogen yield in the milli-scale reactor have been studied. The results indicate that up to 80% of the theoretical hydrogen can be produced from 2 mg (0.053 mM) of NaBH4 using a 6 N HCl solution at a flow rate of 1 mu L/min. The hydrolysis of NaBH4 produces byproducts, such as NaBO2 and NaCl. Acidified water increases the porosity of the interfacial reaction zone consisting of byproducts. This improves liquid delivery to unreacted NaBH4 and results in greater hydrogen generation over longer durations.