When electrolytic solutions or colloidal sols are available only in small quantities, the immersible electrode system required for conductivity measurements on the solution should be small enough to be compatible with the volume of the test solution. To meet this requirement, a probe is described which is sufficiently small for complete immersion in a test solution of about 2*10^-3 cm³ in volume. This probe consists of a single-piece miniature structure formed by a cylindrical capacitor with a central conductor that leads through a ceramic dielectric and a metallic cylinder which coaxially sleeves the outer surface of the ceramic. A protrusion of the inner conductor and the outer sleeving jointly constitute the two-electrode probe. When immersed in an electrolytic solution or a sol and excited by an AC source, the admittance of this capacitive probe would change which can be measured and related to the solution or sol conductivity. Design considerations involved in the construction of the probe and the associated measuring circuits to get optimum performance are discussed. Experimental results obtained from a test probe are presented and discussed.