Horseradish peroxidase biosensors highly sensitive to hydrogen peroxide were constructed with N-methyl phenazine as mediator and coimmobilization of N-methyl phenazine, bovine serum albumin and glutaraldehyde. The sensor possesses perfect stability and high sensitivity, and its linear range is from 1x10(-6) to 5x10(-4) mol/L with the response time of less than 10 s.