Objective To investigate the perioperative changes of serum brain natriuretic peptide (BNP) concentrations in patients undergoing cardiac valve replacement. Methods There were 20 patients admitted to the study, the serum BNP concentrations were measured before cardiac surgery, 24 hours, 7days, 14 days, and 30 days after operation. The preoperative NYHA cardiac function and the left ventricular ejection fraction(LVEF) were measured by echocardiogram. Results The preoperative BNP level was the baseline, it elevated markedly and acutely to a peak value 24 hours after operation ( P =0.003), then the BNP decreased 7 days later, but was still higher than the concentration before operation ( P =0.015), 14 days later it reached to the concentration before operation, 30 days later it was mild lower than preoperative BNP level, but there was no significant difference. There was a positive correlation between NYHA and BNP ( r =0.69, P lt;0.05), but no correlation between LVEF and BNP( r =0.29, P gt;0 05). Conclusion The preoperative serum BNP concentration can reflect the preoperative cardiac function in patients undergoing cardiac valve replacement, the high BNP level indicates the poor cardiac function. The BNP sharply elevated in the early time after operation, then gradually decreased in the late phase postoperation.