The long-term stability of sensing interfaces is an important issue in biosensor fabrication. A novel stable gold nanoparticle (AuNP)-modified glassy carbon (GC) electrode interface (GC-Ph-AuNP)-based biosensor for detecting carcinoembryonic antigen (CEA) was developed. GC electrodes were modified with 1,4-phenylenediamine to form a stable layer, and then AuNPs were bound onto the GC electrodes through CAu bonds. Anti-CEA was directly adsorbed on AuNPs fixed on the GC electrode. The linear range of the immunosensor was from 10 fg to 100 ng mL(-1) with a detection limit of 3 fg mL(-1) (S/N=3). The current of the immunosensor was increased by 4% after one month. The GC-Ph-AuNP immunosensor showed high sensitivity, a wide linear range, low detection limit, and good selectivity and stability. The immobilization method of the immunosensor could be widely applied to construct other immunosensors.