in this research strained yoghurts were made from different acidity yoghurts and milk with and without added natamycin. The effects of addition natamycin, different acidity and storage time of strained yoghurts on shelf life were investigated at 4°C for 15 days. The addition of natamycin had a significant effect on yeast and mould counts (p< 0.05) and no effect was found on chemical, physical and sensory properties of strained yoghurts (p> 0.05). The use of different acidity yoghurts had a significant effect on the final acidity value of strained yoghurts (p< 0.05) but no effect was found on pH, asetaldehit, lactose, penetrometer, tirozine and yeast and mould counts of strained yoghurts (p> 0.05). The acidity of strained yoghurt was increased and pH was decreased during storage (p< 0.05). Lactose value of yoghurt were decreased (p< 0.05). Moreover, the changes in asetaldehit, tirozine and penetrometer value of strained yoghurt were found to be significant during storage (p< 0.05). The results also showed that the difference in appearance consistency and total scores of sensory properties were found to be significant (p< 0.05), and the difference in taste and aroma scores were found to be not significant (p> 0.05).