Objective To evaluate transvaginal ultrasonography in diagnosis of ovarian serous cystdenoma and explore the possibility of higher accurate rates of diagnosis. Methods The findings of transvaginal ultrasonography were analyzed in 33 patients with ovarian serous cystdenoma proved by surgery, and the diagnostic accuracy was discussed. Results All the thirty-three patients with ovarian serous cystdenoma were single, 23 of whom had unilocular cysts and 20 were diagnosed accurately by transvaginal ultrasonography. The accurate rate was 86.9%（20/23）. The other ten had multilocular cysts,six of whom were diagnosed accurately by transvaginal ultrasonography. The accurate rate was 60%(6/10). Conclusion Transvaginal ultrasonography can contribute more to the diagnosis of ovarian unilocular serous cystdenoma than to multilocular ones, especially those with spottyechoes in the cystic liquid.