Subcutaneous injection of low-molecular-weight-heparin (LMWH) at home was done for whole gestational period in a 31 year-old female patient with a mechanical prosthetic valve in the mitral position (St. Jude 23 mm). Anti Xa activity and aPTT were regularly monitored once a month, and dosage of LMWH was adjusted to maintain anti Xa activity between 0.6-1.0 IU/ml. Transthoracic echocardiography was performed to check function of a mechanical prosthesis, especially the opening and motion of mechanical bileaflets. Without fetal loss, embolic episode or thrombotic complication, full-term vaginal delivery of a healthy girl could be obtained. LMWH with cautious monitoring of mechanical prosthesis using echocardiography can be a safe, practical and rational option for pregnancy in patients with mechanical prostheses.