An experimental study on column thickness variation of 100-mu m liquid jets and mean liquid breakup lengths in still air at standard temperature and ambient pressure is described. Jet exit conditions used were limited to short length/diameter ratio of 0.75, jet exit Reynolds numbers (Re-L) of 2500-5800, jet exit Weber numbers (We(L)) of 900-4900, and liquid/gas ratio of 690. These exit conditions yielded liquid jets with rapid variation of cross-sectional area along the jet axis. The digital holography and image processing were performed in the following four phases: (1) digital microscopic hologram (DMH) recording, (2) numerical reconstruction of recorded holograms, (3) image segmentation, and (4) column diameter measurement. The variation of cross-sectional column thickness of 100-mu m liquid jets was expressed by four characteristic diameters: LCD (local column diameter), ALCD (averaged local column diameter), VCD (volumetric column diameter), and AVCD (averaged volumetric column diameter). In this study, the normalized AVCD was used as the contraction coefficient for calculating discharge coefficients. The mean breakup lengths of 100-mu m liquid jets were found to be a function of jet exit Weber number. The present results of 100-mu m liquid jets were comparable to previous results for macro liquid jets.