We present a label-free detection of swine influenza virus (SIV) H1N1 by means of the excellent electrical properties of single-walled carbon nanotubes (SWCNTs). The electrical resistance of SWCNT resistor tends to increase upon the surface adsorption of macromolecules such as poly-L-lysine, anti-SIV antibodies, and SIVs in the process of immunoassay. The SWCNT network resistor was successfully able to detect as low as 180 TCID50/ml of SIV using the resistance shifts upon immunobinding of SIVs. The sensor specificity was demonstrated against transmissible gastroenteritis virus (TGEV) and feline calicivirus (FCV). This facile CNT-based immnoassay has potential applications as a rapid point-of-care detection or a sensing platform for lab-on-a-chip systems.