Breakage phenomena observed in a novel interfacial polymerization reactor was characterized by a breakage parameter （t_b/t_m） which can be interpreted to be the ratio of the breakage time divided by the mean residence time. This parameter was calculated from the equation relating the mean fibrid sizes in the product and the initial streams. The usefulness and validity of the analysis were checked bycomparing the calculated variance of the product distribution against experimental data. The breakage parameters obtained from the 25 gallon unit data were also related to the reactor volume and r.p.m. by nonlinear regression analysis.