The detection of human fibrin has been performed by immunological piezoelectric quartz crystal microbalance technique. Anti-fibrin antibody was immobilized onto the gold electrodes of a 9 MHz AT-cut piezoelectric quartz crystal with bovine serum albumin adsorption, followed by glutaraldehyde cross-linking. The antibody-bound crystals had good response to human fibrin in the concentration range of 10−4∼10−1g/L. The sensor system had good selectivity. The crystal could be regenerated nearly 10 times without detectable decrease of sensitivity.