〔Abstract〕 Objective To explore a new serum marker of carotid artery plaque instability——pregnancy-associated protein-A(PAPP-A) and to evaluate its prognosis in patients with ischemic stroke. Methods 84 patients with ischemic stroke were selected and divided into stable plaque group and unstable plaque group according to carotid ultrasound examination. Then the serum levels of PAPP-A were compared between the two groups. Besides, the National Insititutes of Health stroke scale(NIHSS) scores and activity of daily living scale(ADL) scores of the two groups were assessed respectively at three timepoint: before treatment, the 4 th week and 12 th month after treatment during 1 year's following up. Simultaneously, the changes of the scores were compared, to explore their roles in evaluating the prognosis of patients with ischemic stroke. Results The serum levels of PAPP-A in the unstable plaque group were significantly higher than those in the stable plaque group(P<0.01).The area under the curve(AUC) was 0.811 when assessing the predictive value of PAPP-A towards unstable plaque. The NIHSS scores in the unstable plaque group was higher than that in the stable plaque group, while there was no statistical difference in ADL scoresbetween the two groups. Conclusion The serum level of PAPP-A is related to the instability of carotid artery plaque.Patients with ischemic stroke with unstable plaques are more likely tohave poor prognosis.Therefore, rigorous clinical follow-up is recommended.