Abstract: To automatically classify bottlenose dolphin's whistles, a method, which is based on syntactic pattern recognition, is presented. Dolphin whistles have typically been characterized in terms of their instantaneous frequency as a function of time, which is also known as "whistle contour". The frequency variation feature of a dolphin whistle is extracted according to its whistle contour. Then, the frequency variation features are used for learning grammatical patterns. A dolphin whistle is classified according to grammatical pattern of its frequency variation feature. Experimental results show that the classification accuracy of the proposed method is 95%. The method can provide technical support for acoustic study of dolphins' biological behavior.