Background: Lymphovascular space invasion (LVSI) is an independent factor that affects the survival of patients with endometrioid carcinoma (EEC). However, few preoperative methods that can predict LVSI. Transvaginal ultrasonography (TVS) is a routine examination performed in patients with EEC. Therefore, the authors sought to assess whether there is a correlation between uterine blood flow resistance index (RI), determined by TVS, and LVSI. Materials and Methods: The authors performed a case-control study to examine patients with LVSI-positive (n = 30) and LVSI-negative (n = 148) Stage I-III endometrial cancer (EC) who underwent hysterectomy-based surgical staging. The risk associated with TVS intrauterine echo flow RI was estimated based on LVSI patterns. Results: Among 178 patients, the mean RI of patients without LVSI was 0.486 ± 0.15 and that of patients with LVSI was 0.581 ± 0.18. Univariate analysis showed that RI was a risk factor for LVSI (p = 0.027). Multivariate logistic regression analysis indicated that RI was not related to BMI, endometrial thickness, or uterine length. Hypertension, endometrial thickness, and length of intrauterine echo may increase risk through changes in RI (p < 0.05). Conclusion: Increased RI in EEC can predict the presence of LVSI. History of hypertension, endometrial thickness, and length of intrauterine echo also influence RI. Preoperative RI measurement is a useful tool for guiding clinical and surgical treatment.