In the present study, we aimed to investigate whether copeptin values on admission are related to left ventricle (LV) systolic function and its improvement at 6 months in ST-segment elevation myocardial infarction (STEMI) patients.In this single-center, prospective observational study, we included 122 STEMI patients from January 2016 to November 2016. LV systolic functions in the form of global longitudinal strain (GLS) in addition to conventional echocardiography parameters were evaluated on admission and at 6-month. Serum copeptin levels were determined using an ultrasensitive immunofluorescence assay.The study population was divided into 2 groups according to median values of copeptin. GLS was significantly lower in patients with high copeptin levels compared to those with low copeptin levels at early stage and 6-month (-16% (16-16.5) vs -15% (15-15.5), P < .001 and -18% (18-19) vs -16% (16-16.25), P < .001, respectively). Copeptin values were negatively correlated with an early and 6-month GLS (r = -0.459 at early stage and r = -0.662 at 6-month). In addition, we observed that copeptin values were negatively correlated with the improvement of GLS at 6-month follow-up (r = -0.458, P < .001 and r = -0.357, P = .005, respectively).Serum copeptin levels in STEMI patients at the time of admission may predict early and 6-month LV systolic function assessed by two-dimensional GLS. To the best of our knowledge, this study is the first to specifically address the relationship between copeptin values and GLS in STEMI patients.