To study the alteration of protein Z (PZ) in patients with cardio-cerebral thrombotic diseases, its clinical significance and relations with FX.PZ and FX:Ag were measured by ELISA, and plasma FX:C by first stage method. In 170 patients with acute ischemic stroke (AIS), 40 acute myocardial infarction (AMI) and 60 healthy adults as contrast, PZ, FX:C and FX:Ag were measured and compared between incipience and recurrence, different ages and genders.In AIS and AMI groups, PZ levels decreased significantly to (940.02 +/- 229.82) microg/L and (1071.44 +/- 180.52) microg/L, respectively \[the contrast group was (2257.97 +/- 479.76) microg/L, P 0.05). No correlation was found in sex with PZ level, FX:C, FX:Ag (P > 0.05).PZ level was significantly decreased in AIS and AMI patients and was negatively related to FX:C and FX:Ag. The mechanism leading to FX increase may partially related with the decreased of PZ. PZ level was different in the primary and recurrent disease and was gradually decreased with the increase of age. Lack of PZ might be a etiological factor of cardio-cerebral thrombotic diseases.