Clay-bearing rocks disintegrate at varying rates, due to slaking, when exposed to moisture. This research aims to develop a durability classification of clay-bearing rocks based on particle size distribution of slaked material, quantified in terms of disintegration ratio (DR). DR is the ratio of the area under the particle size distribution curve of slaked material for a sample, upon completion of the standardized slake durability index test, to the total area encompassing all particle size distribution curves of the samples tested. Although second-cycle slake durability index (Id2) is the most frequently used parameter for classifying the slaking behavior of clay-bearing rocks, it does not consider the range of particle sizes in the slaked material after the test. Compared to Id2, DR accounts for all particle sizes present in the slaked material and provides a better measure of the degree of slaking. The slake durability index test was used to investigate the slaking behavior of samples from 20 different clay-bearing rocks, and Id2 and DR values were determined for all samples. Id2 showed a nonlinear relationship with DR. The relationship was used to develop a durability classification, based on disintegration ratio, as follows: low durability: DR= 0 to 0.20; medium durability: DR= 0.20 to 0.65; medium-high durability: DR= 0.65 to 0.85; and high durability: DR= 0.85 to 1.00. In order to use this classification, one needs to perform a sieve analysis on material left after the slake durability test and determine DR.