Objective To investigate the incidence and risk factors for cognitive deterioration occurred within the first three months after ischemic stroke. Methods A total of 195 patients with acute ischemic stroke were consecutively enrolled in this prospective study. The patients were divided into two groups: cognitive deterioration and non-cognitive deterioration group, according to whether the total scores of mini-mental state examination (MMSE) dropped by more than 2 points from the acute phase (first fourteen days) to three months after stroke, and comparison was made between the two groups. Logistic regression analysis was applied to determine the risk factors for cognitive deterioration within the first three months after ischemic stroke. Results We found that 117 (60.0%) patients were diagnosed with post stroke cognitive impairment (PSCI) in the acute phase of ischemic stroke and 37 (19.0%) suffered cognitive deterioration within the first three months after ischemic stroke. Univariate logistic regression analysis suggested that the deterioration was significantly associated with age, sex, years of education, MMSE in the acute phase, clinical dementia rating scale (CDR) scores in the acute phase and the level of glycosylated hemoglobin at admission (P<0.05). Multivariate logistic regression analysis suggested that age (>70 years old) (RR=2.509,P=0.045), illiteracy (RR=3.038,P=0.011) and the level of glycosylated hemoglobin (RR=1.364,P=0.016) in the acute phase were the risk factors for cognitive deterioration within three months after ischemic stroke,and high score of MMSE was a protective factor for cognitive deterioration within three months after ischemic stroke (RR=0.852, P=0.001). Conclusion The risk factors for early-stage cognitive deterioration after ischemic stroke include age (>70 years old), illiteracy, high level of glycosylated hemoglobin and serious cognitive impairment in the acute phase.