Abstract: The basalt fiber (BF) was modified with oxalic acid and FeSO₄7H₂O as the raw materials by liquid phase deposition method. The basalt fibers before and after being modified were characterized by SEM, EDS, XPS, contact angel analyzer and Zeta potential analyzer to observe the micro-morphology, elemental composition, hydrophilic and electronegativity. The toxicity of basalt fiber was evaluated by the growth curves of bacillus subtilis in different environment and the impacts of basalt fiber modified with ferric oxalate (MBF) on microorganism adhesion were evaluated by pure adhesion and activated sludge immobilization tests. The results show that the hydrophilic and electronegativity are significantly improved, the water contact angle of MBF decreases from 89.71° to 56.74° and the Zeta potential of MBF increases from -18.53 mV to -5.03 mV by comparison with BF. The MBF do not inhibit bacteria growth and possess no bacterial toxicity. The amount of sludge immobilized onto MBF is 27.91 gm^-2 after 12 h, indicating that ferric oxalate could promote more biomass adhering on MBF surface, thus being favor to the improvement of the effect of waste water treatment.