FOLLOWING the recovery of several fragments A of a very small adult skull of Sinanthropus from Locus I (Locality 1) in the latter part of our spring field season at Choukoutien, we had the good fortune during the fall season of this year to unearth three additional more or less well-preserved skulls, two of which were recovered on one day. All three skulls belong to adult individuals. The skull recovered first, and designated as Skull I of Locus L (Fig. 1), is the largest, with a cranial capacity of approximately 1,200 c.c. and with its coronal and sagittal sutures partly fused. The second skull (Skull II of Locus L, Fig. 2) is the smallest of the group, with a cranial capacity not higher than 1,050 c.c., and its coronal, sagittal and lambdoid sutures fused. This skull shows a clear indication of the persistence of a metopic suture. The third skull (Skull III of Locus L, Fig. 3) is smaller than Skull I, but larger than Skull II. The cranial capacity of Skull III is approximately 1,100 c.c. Although all the sutures of this skull are still patent, yet other characteristic features make it evident that we are concerned with a young adult individual. Parts of the face are preserved in all three skulls; thus, in Skull III both nasal bones and the entire lateral border of the orbit in complete connexion with the brain case; in Skull II the frontal process of the maxilla, the lower border of the orbit, the cheek-bone and fragments of the alveolar process of the upper jaw with palate and ten teeth in situ (premolars and molars), which, however, are not connected with the skull. Belonging to Skull I are several teeth only. In addition, we have a great number of very small fragments apparently pertaining to the face, yet it is rather doubtful whether it will be possible to undertake even a partial reconstruction.