Hypothesis: Uniform cross-linked cellulase aggregate (XCA) can be prepared by using a millifluidic reactor which consists of two inlets and a Y-junction, because mixing pattern and spatial distribution of reactants can be controlled precisely. Experiments: Aqueous cellulase solution is mixed with acetonitrile (as a precipitant) and 20 mM of glutaraldehyde (as a cross-linker) at the Y-junction. XCA is collected from the outlet of the reactor. Findings: Uniform XCA, with an average size between 200 nm and 400 nm, can be formed inside the reactor. Unlike free cellulase, XCA is insoluble such that it can be filtered out from the solution. It can be used alone or absorb on silica gel (XCA-Si) as a catalyst for hydrolyzing carboxymethyl cellulose (CMC). Interestingly, XCA-Si shows highest activity at pH 4.8 and 50 degrees C, which is similar to the optimal condition of free cellulase. Moreover, XCA-Si is more stable than free cellulase at high temperature (>60 degrees C). It precipitates naturally and can be recycled at least 5 times after the hydrolysis of CMC. (C) 2014 Elsevier Inc. All rights reserved.