Geographical variations of skull among the Yangtze, Yellow Sea and South China Sea populations of the finless porpoise, Neophocaena phocaenoides, in Chinese waters were studied using 42 skull measurements based on 144 specimens (40 from Yangtze population, 59 from Yellow Sea population and 45 from South China Sea population) deposited in the Cetacean Research Laboratory, Nanjing Normal University. The t-test and covariance analysis (Tab.2) demonstrated that: Condylobasal length in the adults of the Yangtze population was shorter than that of the other two populations (Fig. 1). The South China Sea population had shorter rostrum length (Fig.2a), but it had the largest width of rostrum, the Yangtze population had the second,and the Yellow Sea population had the smallest (Fig,2b). The Yellow Sea population was smaller in the width of premaxillaries, zygomatic, preorbital (Fig. 2c) and postorbital.The South 168 China Sea population had more teeth on maxillaries while the Yellow Sea population had more teeth on mandibles.Tooth number of the Yangtze population was relatively smaller.The South China Sea population had also larger width of pterygoids (Fig.2d) and interior nares, but smaller orbital length and preorbital length of lacrimal. The Yangtze population had longer temporal fossa and periotic, wider occipital condyles. The discriminant analysis (Tab.3,Fig.3) showed that: 1) Difference in the skull measurements among the three Chinese populations was demonstrated even for neonates; 2) Difference between the South China Sea population and the other two was larger than that between the Yangtze and Yellow Sea populations. 3) The rostrum length and rostrum width valued by previous authors were not the optimal group of skull characters to distinguish the Chinese populations. Generally, the difference in the skull among different geographical populations was represented by a number of variables. Although we have distinguished the populations using a few external measurements (reported in another paper), we could not do it using a few skull characters. It implies that in the course of population evolution,the osteological adaptation of Neophocaena took place at a slower rate than the external morphology did.