Purpose: The present study was performed to examine the effect of short term consumption of yoghurt containing Lactobacillus rhamnosus on some cariogenic bacteria as Streptococcus mutans and Lactobacilli bacteria. Materials and methods: Forty children were selected from (Awlady) orphanage in Egypt and were divided into two groups (control and intervention). The study consisted of three 3 periods: baseline, intervention (for 3 weeks) and post-treatment (for another 3 weeks). Salivary Streptococcus mutans counts and lactobacilli counts were measured at the 3 different periods and the results were statistically analyzed. Results: The results showed that there is a statistically significant difference between mean SM counts while there was no statistically significant difference between mean LB counts through the three time periods. Conclusion: Short-term consumption of yoghurt containing probiotics might have an inhibitory effect on Streptococcus mutans.