Background: Calcified nodules (CN) have been linked to unfavorable clinical outcomes. However, there is a lack of systematic studies on non-culprit lesions with CN in patients with acute coronary syndromes (ACS). This study aims to investigate the frequency, distribution, predictors, and outcomes of CN in non-culprit lesions among ACS patients. Methods: We included 376 ACS patients who received successful stent placement in their culprit lesions. Intravascular ultrasound (IVUS) was performed to evaluate non-culprit lesions in left main arteries and all three coronary arteries (CA). CN was defined as accumulations of small nodular calcium deposits exhibiting a convex shape protruding into the lumen. Results: CNs was identified in 16.9% (121 of 712) per artery and 26.9% (101 of 376) per patient. They were predominantly located at the mid portion of the right coronary artery (26.3%) and the bifurcation site (59.9%). Patients with CN were older (63.57 \pm 8.43 vs. 57.98 \pm 7.15, p 0.001) and had a higher prevalence of diabetes mellitus (55.4% vs. 42.2%, p = 0.022). However, there were no significant differences in baseline characteristics observed after propensity score matching (PSM). Multivariate analysis revealed that CN were independently associated with major adverse cardiovascular events (MACE) both before and after PSM (hazard ratio (HR): 0.341, 95% confidence interval (95% CI): 0.140–0.829, p = 0.018; HR: 0.275, 95% CI: 0.108–0.703, p = 0.007, respectively). During the observational period of 19.35 \pm 10.59 months, the occurrence of MACE was significantly lower in patients with CN before and after PSM (5.9% vs. 16.7%, p = 0.046; 4.0% vs. 18.1%, p = 0.011; respectively). Conclusions: CN in non-culprit lesions with ACS patients was prevalent and caused fewer adverse clinical outcomes.