Abstract: In order to research the relationship between tooth and body size in Phayres leaf monkey,the distance from glabella to opisthocranion was chosen to represent the body size (Wood,1979).The conclusions show that Phayres leaf monkey incisors exhibit significant negative correlationship and allometry with increase of the body size.Molars,especially those in the mandibula,are isometry or nearly isometry with the increase of body size.These phenomena are tightly correlated with their feeding habits.That is,the diets in this kind of animal mostly include the leaves and seeds which make them to use the molars in chewing frequently (chew carefully and swallow slowly) the hard fibers.There is much correlated with the body size on the buccolingual distance than that on the mesiodistal distance because the allometry coefficients on the buccolingual distance are significant bigger than those on the mesiodistal distance.So we hypothesize when Phayres leaf monkeys use molars to chew the leaves and seeds the movement usually happens in the direction from right to the left or from buccal to lingual direction.The relationship between the tooth and body size in Phayres leaf monkeys is closer to that of Colobus guereza,than to the human.These show that in the evolutionary process,phylogeny and feeding habits,Phayres leaf monkey is more closer to that of Colobus.