Objective To investigate the relationship of admission hyperglycemia with changes in infarct volume and in-hospital outcome (within 1 week after onset) in the elderly patients with acute ischemic stroke after the treatment of recombinant tissue plasminogen activator (rt-PA). Methods All consecutive elderly patients suffering from acute ischemic stroke and treated with rt-PA within 3h after onset in our hospital from 2010 to 2013 were enrolled in the study. They were divided into hyperglycemic group and normoglycemic group according to their blood glucose levels at admission. The recanalization and infarct volume at different time points after onset were evaluated with magnetic resonance scanning. The National Institute of Health Stroke Scale (NIHSS) scores of different time points were also evaluated and compared between the 2 groups. Results There were totally 44 patients enrolled in the study, and 24 of them had admission hyperglycemia. There was no difference in initial infarct volume between the normoglycemic and hyperglycemic groups [(29.5±56.2) vs (28.3±61.7), P＝0.90]. However, hyperglycemic patients had higher admission NIHSS scores [(17.7±6.6) vs (12.9±6.3), P＜0.01]. No difference was seen in the recanalization and hemorrhage rate between the 2 groups at 24h after onset. In 24h and 7d after onset, hyperglycemic patients had larger stroke volume [(121.7±101.1) vs (68.8±85.4), P＝0.03; (170.8±163.9) vs (92.5±113.6), P＝0.02], and higher NIHSS scores than normoglycemic patients [(14.3±6.9) vs (8.6±5.1), P＜0.01; (8.8±7.4) vs (4.3±3.9), P＜0.01]. Hyperglycemic patients also had higher rate of poor prognosis at 7d after onset than normoglycemic group patients (42% vs 15%, P＝0.05). Conclusion Admission hyperglycemia does not interfere the early recanalization and safety of rt-PA thrombolysis, but it is associated with in-hospital infarct volume expansion and poor outcome in the elderly acute ischemic stroke patients.