The performance of the electrical aerosol analyzer (EAA) for aerosol number and volume concentration measurements has been evaluated using polydisperse aerosols of sucrose, NaCl, (NH4)2SO4, dioctyl phthalate, and H2SO4. Comparisons were made between the EAA and a General Electric condensation nuclei counter (CNC) for aerosol number concentration measurement and with a gravimetric analysis technique for aerosol volume or mass concentration measurement. For number concentration measurements, it has been found that the EAA agrees with the CNC, the systematic difference between the two instruments being negligible and the random difference being about 5–10%. For volume concentration measurements, the maximum discrepancy between the EAA and the gravimetric technique is about ±20% for spherical particles in the 0.04- to 0.4-μm-diameter range. The discrepancy increases to about 30% for spherical particles of 0.55-μm diameter. This is attributed to the limited size resolution capability of the EAA near the upper limit of the instrument. For nonspherical particles, a discrepancy as large as 60% has been observed between the EAA and the gravimetric technique. It is concluded that the difference between the “equivalent sphere” diameter measured by the EAA and the “equivalent sphere” diameter based on particle volume may be as much as 20% for the nonspherical particles used in the study. Thus, one should exercise caution in using the “equivalent sphere” diameter measured by different instruments for calculating various aerosol properties.