Previous studies showed that both inflammation and platelets have a role in development of slow coronary flow (SCF). Platelet to lymphocyte ratio (PLR) as an emerging inflammatory indicator was significantly associated with adverse cardiovascular events. Therefore, we aimed to assess the relationship between PLR and SCF. Patients who had angiographically normal coronary arteries were enrolled in this retrospective study (n = 221 as SCF group and n = 293 as control group). Patients who had thrombolysis in myocardial infarction frame counts (TFC) above the normal cutoffs were considered to have SCF. Both PLR and C-reactive protein (CRP) were significantly higher in the SCF group. In correlation analysis, PLR has a significantly positive correlation with the left anterior descending artery TFC (P = .001), circumflex artery TFC (P < .001), right coronary artery TFC (P < .001), and serum CRP level (P < .001). In multiple logistic regression analysis, PLR was independently associated with presence of SCF (odds ratio: 1.014, P < .001). In conclusion, higher PLR levels were significantly and independently related to the presence of SCF. Besides, PLR was positively correlated with serum CRP level as a conventional marker for systemic inflammation.