Freeze drying is now the most common preservation method for industrially important microbial cultures. In this method, choice of cryoprotectant type has direct effect on survival of microorganism. In this study, four industrially important microorganisms were dried by this method. The purpose of this study was evaluation of the protective effects of Persian gum, gum Arabic and skim milk powder on survival of Lactobacillus plantarum A7, Escherichia coli , Xanthomonas axonopodis and Saccharomyces cerevisiae during freeze drying. For this purpose, after activation of cultures and cells were harvested from early stationary phase of microbial culture using centrifuge and after washing cells with saline, it was diluted and enumerated by milse misra method. Solutions of Persian gum, gum Arabic, skim milk powder and combination of them were prepared and sterillised. Bacterial suspensions were mixed with cryoprotectant solutions and after homogenization were poured into vials and were frozen in the freezer at -80 ?C and then were dried in freeze-dryer. Survival rate was evaluated immediately after freeze drying and 14 days of cold storage (4 ?C). Protective effects of Persian gum 1% (W/V) compared with that of gum Arabic 5% (W/V) and 10% (W/V) and skim milk powder 10% (W/V) showed no significant difference on survival of Lactobacillus plantarum A7 (P 0.05). In addition, no significant differences (P 0.05) were observed between protective effect of Persian gum 6% (W/V) compared with that of gum Arabic 6% (W/V), combination of Persian gum 3% (W/V) and gum Arabic 3% (W/V) and skim milk powder 10% (W/V) on survival of Escherichia coli whereas effect of skim milk powder 10% (W/V) on survival of Xanthomonas axonopodis and Saccharomyces cerevisiae was significant (P 0.05). After 14 days of storage (4 ?C), effect of Persian gum 6% (W/V), on survival of Escherichia coli and effect of gum Arabic 6% (W/V) on survival of Xanthomonas axonopodis and Saccharomyces cerevisiae were observed to be statistically significant (P 0.05). In conclusion, Escherichia coli , Xanthomonas axonopodis and Saccharomyces cerevisiae were less resistant to freeze-drying compared with Lactobacillus plantarum A7, even though the higher concentration of Persian gum and gum Arabic were used to protect them. ersian gum for Escherichia coli and skim milk powder for Xanthomonas axonopodis and Saccharomyces cerevisiae , could replace other cryoprotectants. Persian gum 6% (W/V) for Escherichia coli , gum Arabic 6% (W/V) for Xanthomonas axonopodis and Saccharomyces cerevisiae , seemed to be the best protective agents during 14 days of storage. Persian gum 1% (W/V) may also be used as an alternative protective agent instead of skim milk powder 10% (W/V) and gum Arabic 5% (W/V) for freeze drying of Lactobacillus plantarum A7. As Iranian Persian gum is cheaper and seems to have similar performance to gum Arabic and skim milk powder at lower concentration, therefore could be considered a better choice for industrial applications. Key‌ words: Escherichia coli , freeze dying, gum Arabic, Lactobacillus plantarum A7, Persian gum, Saccharomyces cerevisiae , skim milk powder, Xanthomonas axonopodis .