Abstract: β-Amylase (E.C. 3.2.1.2) from Fonio millet Acha Digitaria exilis was purified by acid treatment, anion exchange chromatography on DEAE cellulose and gel filtration on Sephadex G-100. The pH and temperature optima were 6.0 and 50°C, respectively using soluble starch as substrate. The enzyme was active within the pH range of 4.0 -10.0 and was most stable between 30 and 50°C. The Km value for soluble starch was 5.892 mg mL-1. The activation energy for catalysis by Digitaria exilis β-amylase was 10.49 kJ mol-1. The free energy change (∆G#), enthalpy change (∆H#) and entropy change (∆S#) for inactivation were 53.18, 23.7 and-101.02 kJ mol-1, respectively. The enzyme was activated and stabilized by Na+ and Ca2+ and inhibited by Hg2+ and EDTA. pH dependence of the temperature stability of the enzyme was studied in the temperature range of 40 - 70°C at pH 5.0, 6.0, 7.0 and 8.0. The pH dependent thermal activation was investigated between 25-50°C at 5.0-8.0 pH. At pH 6.0 the activation energy (Ea) for Digitaria exilis β-amylase was 10.49 kJ mol-1 while the activation enthalpies (∆H#) and activation entropies (∆S#) were 8.01 and –96.12 J mol-1K-1 at 25°C, respectively. The result showed that thermal stability and thermal activation were pH dependent. Digitaria exilis seed β-Amylase was very stable at alkaline pH and neutral pH at higher temperatures of 60 and 70°C but less stable at acidic pH of 5 and 6. Thermodynamic activation parameters derived from thermal activation data suggested the reaction was faster at pH 6. The thermodynamic data also suggest that hydrogen bond might play a role in stabilization of the enzyme at higher temperature in alkaline medium. The enzyme recovered 68% of its original activity following renaturation brought about by the removal of the 4 M guanidine hydrochloride, the denaturing agent.