We report the detection of protein molecules with nanofabricated pores using the resistive pulse sensing method. A 20-nm -thick silicon nitride membrane with a nanofabricated pore measuring about 55 nm in diameter separated an electrolyte cell into two compartments. Current spike trains were observed when bovine serum albumin (BSA) was added to the negatively biased compartment. The magnitude of the spikes corresponded to particles 7-9 nm in diameter (the size of a BSA molecule) passing through the pore. This suggests that the current spikes were current blockages caused by single BSA molecules. The presented nano-Coulter counting method could be applied to detect single protein molecules in free solution, and to study the translocation of proteins through a pore. © 2006 American Institute of Physics.