The authors report an in-situ quartz crystal microbalance (QCM) method to measure the outgassing from resist materials during VUV light exposure using 146 nm light. The sensitivity of the present QCM system was 1 ng. The weight of resist film on quartz crystal decreased with irradiation time. The weight loss corresponds to the amount of outgassing from the resist films. The outgassing from KrF, ArF and F/sub 2/ resists during exposure was measured. The outgassing rate was strongly dependent on the structure of resist polymers, in the order: methoxymethyl < t-butoxy < t-BOC < ethoxyethyl, and on the alkyl group structure of the ester units, in the order: adamantyl < isobornyl < isopropyl < methyl < t-butyl.