A new bronchial dosimeter has been proposed which consists of only a single sampler and employs only one 400 mesh wire screen and one filter. During sampling air is drawn through the screen and filter at a face velocity of 12.0cm/s. After sampling the measurements of the screen and filter are made

respectively

by gross alpha counting. The annual effective dose （AED

in mSv/a） is then calculated in the tracheobronchial （T-B） region exposed by radon progenies. The dosimeter can be used in conjunction with an activated charcoal canister for measurements of the radon gas concentration to yield the effective dose conversion factor （DCF

in mSv/a per Bq/m3）. The validity of the dosimeter has been tested through measurements of the AED and DCF under different environments. A design of the portable bronchial dosimeter is given.