Giardia duodenalis is a parasite that causes gastrointestinal diseases and is widespread worldwide. This parasite, which causes infections especially in lambs, is highly prevalent in farm animals. In this study, the prevalence and risk factors of G. duodenalis in lambs were investigated. Lamb fecal samples were collected during the study and microscopic and molecular examinations were performed using Nested PCR method. While Giardia sp. cysts were detected in 28 (23.33%) of 120 samples, the DNA of the parasite was detected in 35 (29.17%) of 120 samples by molecular examination. At the end of the study, the prevalence of G. duodenalis in lambs was recorded between 23.33% and 29.17%. The highest prevalence rate among age groups was found in 16-30 days old lambs, while the highest positivity rate among locations was found in Şirvan district and the lowest positivity rate was found in the center. According to gender, the disease prevalence was higher in females than in males. However, there was no statistically significant difference between location, gender and age groups (p>0.05). In conclusion, G. duodenalis infestations are commonly found in lambs in Siirt province. The results of this study emphasize that control measures and hygiene practices should be implemented to prevent and control G. duodenalis infestations in lambs.