Purpose: Post-stroke cognitive impairment (PSCI) is common among stroke survivors, although its risk factors are not well understood. Here, we assessed cognitive function in patients within 14 days after minor stroke and investigated the risk factors of PSCI, including sleep-related factors. Methods: Patients with minor acute ischemic stroke (n = 86) were continuously recruited from November 2015 to October 2016. Demographic and clinical data were collected, and cognitive assessment and polysomnography were performed. Based on their cognitive performance, stroke patients were divided into PSCI and no PSCI groups. Age-, sex-, and education-matched participants (n = 36) were included as a healthy control (HC) group. Results: Stroke patients showed impairments in multiple cognitive domains relative to HC participants (p < 0.01). Among stroke patients, the prevalence of PSCI and obstructive sleep apnea was 81.4 and 74.4%, respectively. Impairments in attention and working memory (87.1%) and executive function (84.3%) were the most common among stroke patients. Compared with no PSCI patients, PSCI patients showed a higher prevalence of obstructive sleep apnea (50.0 vs. 80.0%, p = 0.030) and shorter total sleep time (435.1 ± 104.0 vs. 347.3 ± 98.1 min, p = 0.002). Logistic regression analysis showed that education duration, total sleep time, and lowest SaO2 were independent risk factors for PSCI. Conclusions: The prevalence of PSCI is high after minor ischemic stroke. In particular, attention and working memory and executive function are most commonly impaired. Although the risk factors for PSCI are numerous, shorter total sleep time and degree of hypoxia at night warrant further attention. © 2018, Springer Nature Switzerland AG.