Microwave application technologies such as microwave heating., microwave assisted chemistry., etc. are of the innovative green technologies. In this paper., a 5.8 GHz microwave applicator of medium size is proposed based on the post-wall waveguide structure. It is allowed to irradiate microwaves to solvent of several milliliters and to flow the heated solvent out continuously. The validity of the proposed applicator is examined numerically and experimentally with microwave power sources of about 5 W.