The hydrolysis mechanism of polyamide I I for offshore applications has been investigated in detail. Very careful experimental procedures have been developed to avoid any overlaying oxidation reactions. During hydrolysis the main mechanism is chain scission of polyamide 11. The experimental results are well described by a kinetic model. derived from the reaction of polyamide I I with water. This model predicts the molecular weight evolution of polyamide I I hydrolysis in pure water.