Purpose: to evaluate the effect of labor on pelvic floor muscles strength. Methods: Two hundred pregnant women at beginning of the 9 th month of pregnancy were selected randomly from antenatal care clinic of Kasr Al-Aini University Hospital in Cairo, Cairo University. Their ages were ranged from 25 to 35 years old and their body mass index was not exceeding 35 kg/m 2 . They were Primigravida and Multigravida. Women who had history of pelvic disease, any previous pelvic operations, diabetes mellitus, history of abortion and history of preeclampsia or smokers and alcohol abusers are excluded from the study. 133 women delivered normal labor (55 primipara and 78 multipara) (Group A) and 67 women delivered by cesarean section (29 primipara and 38 multipara) (Group B). Pelvic floor muscles strength was evaluated for all women by using TG Myo feedback 420v at beginning of the 9 th month of pregnancy and after 6 weeks postnatal. Results: Results of this study found that there was a statistically highly significant decrease (P<0.01) in pelvic floor muscles strength in both groups A and B after 6 weeks postnatal with percentage of decrease 30% and 9% respectively. After 6 weeks postnatal there was a statistical high significant difference between the mean value of pelvic floor muscles strength between both groups A and B with more decrease in group A . Conclusion: It can be concluded that normal labor markedly decreases the pelvic floor muscles strength than cesarean section delivery.