Technical Abstract: The hemicellulose xylan constitutes a major portion of plant biomass, a renewable feedstock available for conversion to biofuels and other bioproducts. ß-xylosidase operates in the deconstruction of the polysaccharide to fermentable sugars. Glycoside hydrolase family 43 has been identified as a source of highly active ß-xylosidases. Biochemical details of four GH43 ß-xylosidases are examined here. Sedimentation equilibrium experiments indicate the quaternary state of three of the enzymes are monomer, homodimer, or homotetramer. kcat and kcat/Km of the four enzymes are higher for xylobiose than for xylotriose, suggesting that the enzyme active sites comprise two subsites, as has been demonstrated by the X-ray structures of some GH43 ß-xylosidases. Ki values for D-glucose (83.3 to 357 mM) and D-xylose (15.6 to 70.0 mM) of the four enzymes are moderately high. The four enzymes display good temperature (Kt^0.5^ ~ 45 °C) and pH stabilities (>4.6 to <10.3). At pH 6.0 and 25 °C, the enzyme from Lactobacillus brevis ATCC 367 displays the highest reported kcat and kcat/Km on natural substrates xylobiose (407 s^-1^, 138 s^-1^mM^-1^), xylotriose (235 s^-1^, 80.8 s^-1^mM^-1^) and xylotetraose (146 s^-1^, 32.6 s^-1^mM^-1^).