Two major components of rRNA (18S and 28S rRNA) were separated by electrophoresis in injection-molded acrylic chips with a microchannel 100 microm in width, 40 microm in depth, and with 1 cm of separation distance. Microchannels were filled with 4 g/L hydroxypropylmethylcellulose as sieving polymer and 5 mg/L ethidium bromide for RNA staining. The fluorescent signals were detected by a fluorescent microscope equipped with a photometer and 590 nm emission filter. The assay is rapid (<3 min), reproducible, RNase-free, and requires only 1-2 microL of sample. The detection limit was approximately 10 mg/L (10 ng/microL), 100-fold lower than that for conventional agarose gel electrophoresis. Because only 0.1 nL of the loaded sample was used for electrophoresis, the detectable peaks of rRNA in the separation were derived from less RNA than in a single cell. Because the quality of RNA is critical for RNA-related diagnostic tests, disposable plastic chips will be useful for quality assessment of RNA.