The present thesis objective is to study noun categorization and the cognitive process associated with noun categorization by classifiers in Thai. Data was gathered via interviews with 50 Thai undergraduate students. The theory of idealized cognitive models, or ICMs, is employed for data analysis. Result show that Each of classifiers categorizes nouns into class(es) with respect to each ICM(s) of classifier. The system of Thai classifier system in this study consist of 4 types ICMs including classical taxonomy model, simple model, complex model, and radial category model. Human classifier group categorize into various classes according to social and cultural conditions such as social class, respectableness, age, gender, and Buddhism. Classifier /khon/ categorizes nouns as humans with respect to animate taxonomy model. Classifier /thân/ categorizes nouns as respectable persons with respect to complex model in which age model, good‐respect model, status model, and knowledge‐capability model combine to form a cluster model. All these individual models in the cluster characterize the concept of RESPECTABLENESS OF PERSON. Respectively, classifier /nai/ and classifier /nang/ categorize nouns as typical males and females occupations with respect to simple model which is defined an ICM regarding expectations of certain occupations in accordance with gender. Classifier /ong/, beside, categorizes nouns into 2 classes including Buddhist animates which are at the center and Buddhist inanimates which extended from the center with respect to radial category model. As for animal and plant classifier group also categorize nouns into class(es) with respect to radial category model. Their extensions are motivated by resemblance shape with the central members. Animal classifier /tua/ categorizes nouns into animals which are center, furniture and clothes which are extended from center by resemble body‐shape with animals. All of the plant classifiers such as /dòk/ /tôn/ /bai/ /mèt/ and /lûk/ categorize respectively flowers, trees, leaves, grains, fruits as central members, and they extended to other classes by resemble shape with their central members. It is clear that certain plant parts have salient shape so that they used as a classifier in order to categorize other nouns that have resemble shape.