Background:　Diffusion-weighted　imaging　(DWI)　provides　useful　information　for　the　identification　of　benign　and　malignant　uterine　lesions.　However,　the　use　of　the　apparent　diffusion　coefficient　(ADC)　for　histopathological　grading　of　endometrial　cancer　is　controversial.　Purpose:　To　explore　the　use　of　ADC　values　in　differentiating　the　preoperative　tumor　grading　of　endometrioid　adenocarcinomas　and　investigate　the　relationship　between　the　ADC　values　of　endometrial　cancer　and　the　histological　tumor　subtype.　Material　and　Methods:　We　retrospectively　evaluated　98　patients　with　endometrial　cancers,　including　both　endometrioid　adenocarcinomas　(n　=　80)　and　non-endometrioid　adenocarcinomas　(n=18).　All　patients　underwent　DWI　procedures　and　ADC　values　were　calculated.　The　Kruskal-Wallis　test　and　the　independent　samples　Mann-Whitney　U　test　were　used　to　compare　differences　in　the　ADC　values　between　different　tumor　grades　and　different　histological　subtypes.　Results:　The　mean　ADC　values　(ADCmean)　for　high-grade　endometrioid　adenocarcinomas　were　significantly　lower　than　the　values　for　low-grade　tumors　(0.800　versus　0.962　x　10(-3)　mm(2)/s)　(P=0.002).　However,　no　significant　differences　in　ADCmean　and　minimum　ADC　values　(ADCmin)　were　found　between　tumor　grades　(G1,　G2,　and　G3)　of　endometrial　cancer.　Compared　with　endometrioid　adenocarcinomas,　the　adenocarcinoma　with　squamous　differentiation　showed　lower　ADC　values　(mean/minimum=0.863/0.636　versus　0.962/0.689　x　10(-3)　mm(2)/s),　but　the　differences　were　not　significant　(P-mean=0.074,　P-min=0.441).　Moreover,　ADCmean　for　carcinosarcomas　was　significantly　higher　than　the　value　for　G3　non-carcinosarcoma　endometrial　cancers　(1.047　versus　0.823　x　10(-3)　mm(2)/s)　(P=0.001).　Conclusion:　The　ADCmean　was　useful　for　identifying　high-grade　and　low-grade　endometrioid　adenocarcinomas.　Additionally,　squamous　differentiation　may　decrease　ADCmean　and　ADCmin　of　endometrioid　adenocarcinoma,　and　carcinosarcomas　showed　relatively　high　ADCmean.