Background: Decreased TIMI flow following percutaneous coronary intervention (PCI) is associated with poor clinical outcomes. However, predicting slow TIMI flow after PCI is limited. Herein, we investigated predicting slow TIMI flow based on the lipid core burden (LCB) of target lesion by using near-infrared spectroscopy-intravascular ultrasound (NIRS-IVUS). Methods and Results: This study retrospectively evaluated 636 patients who underwent NIRS-IVUS guided PCI from a single tertiary center registry. Total patients were divided into decreased TIMI flow group (n=90, TIMI 0, 1, and 2) and normal TIMI flow group (n=546, TIMI 3). The extent of LCB in the treatment zone was calculated as the maximal LCB index (maxLCBi) measured by NIRS for each of the 4-mm longitudinal segments in the treatment zone. In three-month composite events including all-cause death, myocardial infarction, stent thrombosis, and re-intervention, decreased TIMI flow group showed worse clinical outcomes compared to normal TIMI flow group (5.6% vs. 1.5%, log-rank p=0.010). To investigate the correlation between TIMI flow and lipid core burden, a receiver-operating characteristic analysis was performed, and a high LCBi group was defined as maxLCBi 4mm ≥353. Multivariate logistic regression analysis revealed that high LCBi group was strongly associated with decreased TIMI flow (OR 2.223, 95% CI 1.341-3.685, p=0.002). Conclusions: High LCBi measured by NIRS-IVUS could be considered an independent predictor for decreased TIMI flow. Furthermore, a high value for LCBi could lead to worse clinical outcomes.