Pelvic organ prolapse disease is a kind of pelvic dysfunction that pelvic organ prolapse from the vagina or anus due to a weakened function of pelvic floor support strength. Levator ani muscle (LAM) play a key role to support pelvic organs location and steady function. Injury, atrophy and degeneration of LAM may cause pelvic organ prolapse and organs dysfunction. Zijta[1] had applied diffusion tensor imaging(DTI) and fiber tractography to pelvic floor in pelvic organ prolapse. The purpose of our study is to investigate the clinical application value of DTI in evaluating the morphology and microstructure of LAM in the patients with pelvic organ prolapse.Twenty-two patients with pelvic organ prolapse and twenty normal volunteers without pelvic dysfunction diseases as control were participated this study and examined on a 3.0T MR scanner (Ingenia, Philips Healthcare, Best, the Netherlands). MRI exam included TSE T2WI and DTI with parameters are as follows: TSE-T2WI: TR/ TE :3746/90ms, Flip angle=90°, 25 slices, slice thickness=3mm, FOV=260×260mm, matrix=260×257; DTI: TR/ TE : 1171 /60ms, Flip angle=90°, 25 slices, slice thickness=3mm, FOV=260×260mm, matrix=3×3×3. The data of DTI were analyzed using MR diffusion tools on an ISP V7 workstation (Philips Healthcare, Best, the Netherlands). Radiologists with at least 10 years experience draw the ROIs of pelvic floor muscles and documented the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of LAM (puborectails and iliococcygeus muscle) and internal obturator muscle. All the resulted parameters were statically analyzed by independent two samples t-test in different groups using SPSS 18.0 package.Detailed statistical results were shown in Table.1. FA values of both puborectails and iliococcygeus muscle in prolapse group were higher than that of normal control group, the FA values of both puborectails and iliococcygeus muscle between two groups showed significant differences; the ADC values of puborectails and iliococcygeus muscle in normal group were lower than that of prolapse group, but no significant differences were found in ADC values of iliococcygeus muscle between the two groups. No significant differences of FA, ADC values in internal obturator muscle values between normal control group and prolapse group. Fiber tractography demonstrated pelvic floor puborectails, iliococcygeus muscle and internal obturator muscle fiber bundle, as shown in Figure.1-4.DTI and fiber tractography had applied in females pelvic floor muscle state analysis and fiber bundle orientation[1], our study tested this technology in detecting levator ani muscle change in pelvic organ prolapse patients, our study found that FA values of LAM in prolapse group were lower and ADC values were higher than the one in normal control group, it makes sense because pelvic organ prolapse patients were accompanied by a certain degree of pelvic floor muscle relaxation, atrophy and fracture performance. The lower FA value could indicate a higher anisotropy level and the higher ADC value might result from a lower aggregation fiber of levator ani muscle. In the prolapse group, the sizes of muscle buddle of LAM were thinner than that of normal group, which demonstrated the LAM change vividly.The patients with pelvic organ prolapse has a certain degree of atrophy and damage of the LAM, DTI and fiber bundle tracing technique could be useful in evaluation of the general morphology and the microstructure changes of the pelvic floor muscle.