The purpose of this report is to investigate the fliud flow and heat transfer in an opposed plane jet in a uniform stream. An air jet heated up to a temperature of thirty degrees above a uniform air stream issues from a nozzle 3.0 mm in width. time histories, power-spectra and cross-correlation functions of velocity and temperature are measured by a hot-wire anemometer, a resistance thermometer and a FFT-spectrum analyzer. Moreover, unsteady motions are visualized by a Mach-Zender interferometer and a high-speed camera. These indicate that there are measurable flappings of the jet, having two modes. The frequencies of the flappings are varied with the ratio of jet velocity and uniform stream velocity.