A 66-kDa thermostable family 1 Glycosyl Hydrolase (GH1) enzyme with beta-glucosidase and beta-galactosidase activities was purified to homogeneity from the seeds of Putranjiva roxburghii belonging to Euphorbiaceae family. N-terminal and partial internal amino acid sequences showed significant resemblance to plant GH1 enzymes. Kinetic studies showed that enzyme hydrolyzed p-nitrophenyl beta-D-glucopyranoside (pNP-Glc) with higher efficiency (K-cat/K-m=2.27x10(4) M-1 s(-1)) as compared to p-nitrophenyl beta-D-galactopyranoside (pNP-Gal; K-cat/K-m= 1.15x10(4) M-1 s(-1)). The optimum pH for beta-galactosidase activity was 4.8 and 4.4 in citrate phosphate and acetate buffers respectively, while for beta-glucosidase it was 4.6 in both buffers. The activation energy was found to be 10.6 kcal/mol in the temperature range 30-65 degrees C. The enzyme showed maximum activity at 65 degrees C with half life of similar to 40 min and first-order rate constant of 0.0172 min(-1). Far-UV CD spectra of enzyme exhibited alpha, beta pattern at room temperature at pH 8.0. This thermostable enzyme with dual specificity and higher catalytic efficiency can be utilized for different commercial applications.