Evapotranspiration (ET) is a vital component of a field water balance. Canopy chambers are a promising method for determining crop ET because they are portable and applicable at a relatively small plot (m2) scale. Although a variety of canopy chamber designs have been proposed, field tests are still necessary to evaluate chamber performance for measuring crop ET. The objectives of this study are (1) to construct and use an improved canopy chamber to measure ET of three crops [corn (Zea mays, L.), soybean (Glycine max), and reconstructed mixed prairie] and (2) to compare the canopy chamber measurements with flux tower results and field water balance measurements (i.e., rainfall, soil water storage, ET and drainage). Three cropping systems including corn/soybean in a corn-soybean rotation, and reconstructed mixed prairie were studied in central Iowa. Canopy chamber daytime measurements were performed on 18 days in 2013 (a relatively dry growing season) and on 15 days in 2014 (a relatively wet growing season). Based on the results, the differences in daily ET and seasonal cumulative ET between canopy chambers and an eddy covariance flux tower over the measurement periods were within 5%, providing evidence that the portable canopy chamber can accurately measured ET. The chamber ET values and field water balance ET values had similar patterns over the 2013 and 2014 measurement periods, and the differences of cumulative results were less than 10%. In conclusion, the canopy chamber was proven to be an effective method for measuring small plot ET.