To understand the possible roles of the hyaluronan synthetase (HAS)/hyaluronan (HA)/CD44 signaling system in the posterior eye segment, we investigated the expression of rabbit HAS isoforms and CD44 mRNA by RT-PCR and the level of HA by using HA assay and immunohistochemistry. HA was detectable in vitreous, retina and choroid. The expression of three HAS isoforms was clearly detected in both retina and choroids. Rabbit choroid showed a significant increase of the HAS2 and HAS3 expression compared with rabbit retina (HAS2 p = 0.0014 < 0.05; HAS3 p = 0.0006 < 0.05). Similarly, mRNA expression of CD44 was detected in both retina and choroids. This evidence may suggest that the HAS/HA/CD44 signaling system is important in maintaining the functional structure of retina and choroid.