Novel composite hydrogels, poly(acrylamide)-sepiolite (PAS), poly(acrylamide/acrylic acid)-sepiolite (PAAS), and poly(acrylamide/itaconic acid)-sepiolite (PAIS) were prepared and used for the immobilization of invertase. The parameters of equilibrium swelling, diffusional exponent, and diffusion coefficient of these hydrogels were calculated from swelling experiments. Invertase was immobilized onto PAS, PAAS, and PAIS and immobilized invertases (PASI, PAASI, and PAISI) were prepared. Optimum pH values for free invertase, PASI, PAASI, and PAISI are found to be 5, 5.5, 4.5, and 6, respectively, and the optimum temperatures were 30, 50, 50, and 35 degrees C for free invertase PASI, PAASI, and PAISI. It was found that K-m values of free invertase, PASI, PAASI, and PAISI were 11.3, 41.0, 94.5, and 56.0 mM, respectively. V-max values were 2 mu mol/min for free invertase, 8.10 mu mol/min for PASI, 1.30 mu mol/min for PAASI, and 0.42 mu mol/min for PAISI, respectively. The invertase immobilized hydrogels showed excellent, temperature, storage, and operational stability.