Highly sensitive protein detection method based on nanoparticles and enzyme-linked immunosorbent assays (ELISAs), named Nano-ELISA, was introduced. In this method, the micro-magnetic beads were modified with monoclonal antibody of the target protein p53. Gold nanoparticles (AuNPs) were modified with another monoclonal detector antibody and Horseradish peroxidase (HRP, for signal amplification). The presence of target protein p53 causes the formation of the sandwich structures (magnetic beads-target protein-AuNP probes) through the interaction between the antibodies and the antigen p53. The HRP at the surface of AuNPs catalytically oxidize the substrate and generate optical signals that reflected the quantity of the target protein. Down to 5 pg mL(-1) of protein was detected in less than 2 h with this method. The detection sensitivity of p53 classic ELISA kit is 0.125 ng mL(-1). This method is as simple as ELISA and has higher sensitivity than ELISA, which can potentially be exploited in clinic. This method can be used to detect protein markers of tumors, nervous system or other diseases for early diagnostics.