Rho-activated kinases (ROCKs) regulate many cellular functions such as proliferation, migration, and smooth muscle contractility, but they are also associated with pathogenesis of many human diseases such as heart failure and hypertension. We used phage display libraries to identify inhibitory polypeptides that bind to the ROCK1 catalytic domain, but do not compete with the ATP-binding pocket, by screening in the presence of high ATP concentrations (1 mM). Peptide7, a promising ROCK inhibitory peptide for both ROCK isoforms, measured at 1.45 ± 0.28 µM for ROCK1 (1–553) and 5.15 ± 1.15 µM for ROCK2. Peptide7 reduced cellular migration in wound healing assays. The binding epitope on ROCK1 was mapped to the flexible activation loop within the catalytic domain. Peptide alanine scanning mutants helped identify critical amino acids to generate optimized Peptide22. This compact ROCK inhibitor facilitated vascular relaxation, blocked neovascularization of endothelial cells, and inhibited MLC phosphatase phosphorylation. Our novel ROCK peptide inhibitors may provide potential treatment of hypertension and PAH progression. Impact statement Rho-activated kinases, known as ROCK(s), are significant signaling components in cells that lead alterations in cellular function. The central role of ROCK in smooth muscle cellular homeostasis makes it an important therapeutic target. Small molecule kinase inhibitors target enzyme active site competing for ATP binding. Although effective, ATP binding active sites are similar among very different kinases, and many small molecule inhibitors suffer from non-specific inactivation which as therapeutics can lead to substantial side effects. Here, we designed experiments to identify ROCK inhibitors that do not target ATP binding, rather develop peptides that inhibit ROCK in the presence of ATP. We identified a peptide that binds the activation loop of the enzyme and effectively inhibits activity. This will allow a development of a new class of drugs with exquisite specificity for the ROCK kinases and potentially revolutionize treatment of high blood pressure, cardiac hypertrophy, and many more diseases.