β-d-Xylosidase/α-l-arabinofuranosidase from Selenomonas ruminantium is the most active enzyme known for catalyzing hydrolysis of 1,4-β-d-xylooligosaccharides to d-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-β-d-xylopyranoside (4NPX), 4-nitrophenyl-α-l-arabinofuranoside (4NPA), and 1,4-β-d-xylobiose (X2) was determined on and off (k non) the enzyme at pH 5.3, which lies in the pH-independent region for k cat and k non. Rate enhancements (k cat/k non) for 4NPX, 4NPA, and X2 are 4.3 × 1011, 2.4 × 109, and 3.7 × 1012, respectively, at 25 °C and increase with decreasing temperature. Relative parameters k cat 4NPX/k cat 4NPA, k cat 4NPX/k cat X2, and (k cat/K m)4NPX/(k cat/K m)X2 increase and (k cat/K m)4NPX/(k cat/K m)4NPA, (1/K m)4NPX/(1/K m)4NPA, and (1/K m)4NPX/(1/K m)X2 decrease with increasing temperature.