In this study, magnetic nanoparticles (MNPs) of maghemite (γ-Fe2O3) were synthesized and characterized. The method of multifactor experimental design and evolutionary operation (EVOP) was used to optimize immobilization of the alcohol dehydrogenase (ADH) enzyme on MNPs. Optimal operating conditions for the immobilization process were determined (γADH = 0.08 mg/mL, 2% glutaraldehyde for surface activation, t = 28 h), and in such conditions, a specific activity of S.A. = 118 ± 6 U/mg and immobilization efficiency of η = 84.97 ± 3.67% were achieved. Compared to the native enzyme, ADH immobilized on MNPs retained 66.45 ± 3.66% of the initial activity. ADH immobilized on MNPs at optimal conditions was used as a biocatalyst for model reaction—NADH oxidation. NADH oxidation was performed in two different magnetic microreactor configurations: (1) microreactor equipped with permanent square magnets and (2) microreactor equipped with an electromagnet and an oscillating magnetic field that enables magnetic particles movement in the microreactor. In the system with the oscillating magnetic field, equal conversion (X = 100%) was achieved in 2-fold shorter residence time.