Protein plays key role in cellular processes and diseases diagnosis [1-3]. This paper reports a label-free detection of proteins through localized surface plasmon resonance (LSPR) and realized Au nanoparticles (AuNPs) immobilized on glass slide. Glass slide is first sonicated with 5% v/v glassware detergent in ultrapure water for 30 mins, and then in ultrapure water for another 30 mins. A 5% v/v aminopropyltriethoxysilane (APTES) solution in ultrapure water is prepared and the glass slide is immersed in the 5% v/v APTES solution for 20 mins. The glass slide is sonicated for 60 mins in ultrapure water. The purpose of the sonication is to remove the multi-layers of APTES which are formed on the glass surface. The silanized glass slide is immersed in AuNPs solution for 40 mins. Finally, the protein solution is added on the surface of the slide. The surface absorption of proteins induces a significant difference of environmental refractive index around the AuNPs. The shift in the wavelength of the LSPR spectra is very sensitive to the change in the surface refractive index of the nanoparticles. The shifts in the LSPR spectra are primarily determined by the volatility and refractive indices of the protein species. In this paper, the LSPR-nanobiosensor is designed and fabricated. The LSPR band responses are measured by a real-time UV–vis spectrometer with a CCD array detector. The response time of the protein–LSPR spectrum is less than 3 seconds and the response is reversible and reproducible.