Thirty randomized samples of sugar materials were collected from different places (Tartous, Damascus, Homs) in Syria for isolation and identification of some yeasts. These yeasts were classified physiologically by API technique to identify the species of Yeasts found in these materials. Results showed that the isolated materials contained 17 isolated yeasts distributed in 3 genus and 7 species and named as follows: One isolated yeast from Geotrichum capitatum, Candida krusei,Candida guilliermondi, Candida fumata and Candida zeylanoides and 4 isolated yeasts from Candida lusitaniae and 7 isolated yeasts from Saccharomyces cerevisiae. The classified yeasts were screened to investigate the activity of internal and external invertase produced by them using spectrophotometer at 540 nm. The results showed that there were differences in the ability of yeasts to produce invertase enzyme. Candida Lusitaniae-2 and Saccharomyces cerevisiae-4 were found the best yeasts for production of external invertase, whereas Candida Lusitaniae1 was the best for internal invertase.