A method of the determination of the precipitability of polycaprolactam was established, using phenol-alcohol-water (volume ratio 2:1:1) as the solvent and acetone as the precipitant, 0.2 g of the polymer was dissolved in 10 ml of the solvent at 20℃ and titrated with acetone until turbidity began to appear. The calculated precipitabilities gave a linear function with the reciprocal of the molecular weights obtained from carboxyl group titration method.