Background: This study compared the effectiveness of dual antiplatelet therapy (DAPT) with clopidogrel-aspirin with that of aspirin monotherapy (AM) in mild-to-moderate acute ischemic stroke considering the risk of recurrent stroke using the Stroke Prognosis Instrument II (SPI-II) score. Methods: This study is a retrospective analysis of data from a prospective, nationwide, multicenter stroke registry database between January 2011 and July 2018. We included patients with mild-to-moderate (National Institutes of Health Stroke Scale score ≤10), acute (within 24 hours of onset), noncardioembolic ischemic stroke. The primary outcome was a 3-month composite of stroke (either hemorrhagic or ischemic), myocardial infarction, and all-cause mortality. Propensity scores using the inverse probability of treatment weighting method were used to mitigate baseline imbalances between the DAPT and AM groups and within each subgroup considering SPI-II scores. Results: Among the 15 430 patients (age, 66±13 years; men, 62.0%), 45.1% (n=6960) received DAPT and 54.9% (n=8470) received AM. Primary outcome events were significantly more frequent in the AM group (16.7%) than in the DAPT group (15.5%; P =0.03). Weighted Cox proportional hazards models showed a reduced risk of 3-month primary vascular events in the DAPT group versus the AM group (hazard ratio, 0.84 [0.78–0.92]; P <0.001), with no interaction between acute treatment type and SPI-II risk subgroups ( P _interaction =0.44). However, among the high-risk patients with SPI-II scores >7, a substantially larger absolute benefit was observed for 3-month composite vascular events in the DAPT group (weighted absolute risk differences, 5.4%), whereas smaller absolute benefits were observed among patients in the low- or medium-risk SPI-II subgroups (1.7% and 2.4%, respectively). Conclusions: Treatment with clopidogrel-aspirin was associated with a reduction in 3-month vascular events compared with AM in mild-to-moderate acute noncardioembolic ischemic stroke patients. Larger magnitudes of the effects of DAPT with clopidogrel-aspirin were observed in the high-risk subgroup by SPI-II risk scores.