In this study, the production of extracellular thermostable ${alpha}$-amylase by newly isolated thermophilic Alicyclobacillus acidocaldarius was detected on LB agar plates containing 1.0% soluble potato starch and incubated at $60^{circ}C$. This extracellular ${alpha}$-amylase was purified to homogeneity by ammonium sulphate precipitation followed by Sephadex and ion-exchange chromatography. The ${alpha}$-amylase was purified to 8.138 fold homogeneity with a final recovery of 58% and a specific activity of 3,239 U/mg proteins. The purified ${alpha}$-amylase appeared as a single protein band on SDS-PAGE with a molecular mass of 94.5 kDa. Non-denaturing PAGE analysis showed one major band associated with enzyme activity, indicating the absence of isoenzymes. A TLC analysis showed maltose as major end product of the enzyme. The optimum assay temperature and pH for enzyme activity were $60^{circ}C$ and 6.0 respectively; however, the enzyme activity was stable over a wide range of pH and temperatures. The ${alpha}$-amylase retained its activity in the presence of the denaturing agents - SDS, Triton X-100, Tween-20, Tween-80, and was significantly inhibited by EDTA and urea. Calcium ions increased the enzyme activity, while $Hg^{2+}$, $Zn^{2+}$, and $Co^{2+}$ had inhibitory effects. The $K_m$ and $V_{max}$ values were found to be 2.9 mg/mL and 7936 U/mL respectively.