An experimental study concerning the performance of a rectangular fin in partially wet condition was carried out. The visual observation of the dehumidifying phenomenon identified four regions, including the fully dry, very fine droplet, larger droplet, and film-like region. The line of dry-wet boundary is usually inclined and the fin temperature distribution is not one-dimensional. The experimental results are different from those assumptions made by analytical approach. The condensate flow pattern of Fs = 8 mm and Fs = 3 mm at a normalized effective velocity is roughly the same, and the corresponding Awet/A is also approximately equal.