Xylanases produced by filamentous fungi have a promissory biotechnological potential and are extensively used in the industry. In a previous study we reported the production of xylanolytic enzymes in Aspergillus phoenicis cultures supplemented with 1% Birchwood xylan and incubated at 25ºC or 42ºC. It was observed that at the higher temperature the enzyme synthesis was modified and the enzymes xylanase and b-xylosidase gained more thermostability (Rizzatti et al. J. Ind. Microbiol. Biotechnol. 31: 88-93, 2004). The aim of the present work was to observe the influence of temperature on the production and biochemical properties of b-xylosidase, using xylose or the synthetic sugar b-methylxyloside as carbon sources. The microorganism was first grown for 72h at 42ºC, in Vogel minimal medium with 1% glucose, under standing conditions. At this time the mycelium was collected and suspended in fresh medium with 0.1% xylose or 0.1% b-methylxyloside, and reincubated at 25ºC or 42ºC for 48h. b-xylosidase activity was determined using p-nitrophenyl-b-D-xylopyranoside in citrate-phosphate buffer (pH 4). After 24h at 25ºC the mycelial mass doubled, either on xylose or in b-methylxyloside media. In contrast, at 42ºC there was not additional growth in cultures supplemented with b-methylxyloside. b-xylosidase was predominantly intracellular and the best production occurred on cultures incubated at 42ºC with b-methylxyloside, for 48 hours, either in standing or shaken cultures. The optimum temperature of the enzyme was about 65ºC, for the enzyme produced at 42ºC, or about 50ºC when it was produced at 25ºC, when xylose was the carbon source. When b-methylxyloside was used the optimum temperature was 65ºC, independently of the culture incubation temperature. Better stability was observed for the b-xylosidase produced at 42ºC on cultures supplemented with b-methylxyloside or xylose. The enzyme retained 80% of activity after 60 minutes of incubation at 65ºC. In contrast, the b-xylosidase produced at 25ºC, using xylose or b-methylxyloside, was completely inactivated at 65ºC.