We developed a wireless electrical conductivity (EC) sensor screening system to evaluate changes in the EC of sensor films. This sensor system was designed to be equipped with a special sensor chip (14 × 40 mm2), and changes in the EC of a droplet containing a sensor film (ϕ3 mm) on the chip were determined. Electrode pairs were fabricated on glass substrates by photolithography, and a well structure was formed around each electrode pair using photoreactive resin. This sensor system achieved parallel detection of EC signals from five wells, each containing 5 μl of solution with a sensor film in 10 s (N = 5). Furthermore, we developed sensor films that displayed the changes in the EC upon the adsorption and/or chemical binding of protein with Na+ as a counterion. To form the sensor films, the surface of cellulose was chemically modified with alkylamino groups. The EC detected the sensor screening system using aminated cellulose with physically adsorbed bovine serum albumin (BSA) and the amount of Na+ ions increased linearly with BSA concentration with a correlation coefficient (R2) of 0.87. Meanwhile, aminated cellulose with chemically bound BSA through polylysine and glutaraldehyde and adsorbed Na+ exhibited an EC that depended on the BSA concentration, with an R2 value of 0.943. The detection limit of BSA was 10 ng/ml for both types of sensor film. On the basis of our results, the mechanism behind the increased sensitivity of the sensor films with immobilized protein in the presence of a counterion was proposed.