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Background: Early and accurate diagnosis of ischaemic stroke (IS) requires the use of an optimized biomarker. Exosomal microRNAs have the potential to serve as biomarkers owing to their stability and specificity. We investigated the expression levels of plasma-derived exosomal microRNA-21-5p and microRNA-30a-5p in the different phases of IS. Methods: One hundred forty-three patients with IS and 24 non-stroke controls were enrolled. The patients were divided into the following 5 groups: 1 group for the hyperacute phase IS (HIS, within 6 h); two for the acute phase IS (AIS, including days 1–3 and days 4–7); one for the subacute phase IS (SIS, days 8–14); and one for the recovery phase IS (RIS, days >14). Plasma exosomes were isolated using a QIAGEN exoRNeasy kit and examined by transmission electron microscopy, nanoparticle tracking, and flow cytometry. The expression levels of miRNA-21-5p and miRNA-30a-5p were detected by quantitative real-time polymerase chain reaction. Results: The plasma exosomal miR-21-5p levels in SIS and RIS were significantly higher than that in controls (p < 0.05 and p < 0.01 respectively). The levels of miR-30a-5p in HIS were significantly higher (p < 0.05) and in AIS (days 1–3) were lower than that in controls (p < 0.05). In AIS (days 1–3), both miRNAs were decreased compared with the HIS group (p = 0.053 and 0.001, respectively). The area under the curve (AUC) of the miR-21-5p was 0.714 for SIS (95% CI 0.570–0.859, p = 0.007), 0.734 for RIS (95% CI 0.596–0.871, p = 0.003); the AUC of the miR-30a-5p was 0.826 for HIS (95% CI 0.665–0.988, p = 0.001), 0.438 for AIS (days 1–3; 95% CI 0.240–0.635, p = 0.516). Conclusions: The plasma-derived exosomal miR-21-5p and miRNA-30a-5p in combination are promising biomarkers for diagnosing IS and distinguishing among HIS, SIS, and RIS, especially miRNA-30a-5p for the diagnosis of the HIS phase. Our results provide a new reference for clinicians to apply in early-stage diagnosis and identifies the possible value of biomarkers for IS thrombolysis therapy.