Cyclic adenosine monophosphate-dependent protein kinase (PKA) and mitogen-activated protein kinase 1 (MAPK1) are critical regulators in cell signaling that control a diverse set of cellular functions, including gene expression, cell cycle progression, tumor suppression, and apoptosis. Dysregulation of these kinases has been linked to many diseases, including cancer, renal disorders, and cardiovascular diseases. We hypothesized that, by modifying the substrate selectivity of PKA and MAPK1, cells may regulate which pathway is activated in response to a given signal. Specifically, we investigated the impact of redox modification on the substrate selection of PKA and MAPK1. To this end, we used surface plasmon resonance (SPR) and fluorescence polarization (FP) spectroscopy to assess the ability of oxidized and reduced forms of PKA and MAPK1 to bind a variety of model peptide ligands (e.g., PKI, Kemptide, and CREBtide for PKA and Lig-D, pepRSK1, and pepMEF2A for MAPK1). The binding of each substrate was monitored in real-time and the apparent rate constants (kon,app, and koff,app) and equilibrium binding parameters (i.e., KD,app) were determined for each kinase-ligand pair. These studies suggest that H2O2-dependent oxidation of PKA and MAPK1 alter their interactions with some ligands while having little effect on others. To gain further insights into the factors driving the differential changes in the interaction between these kinases and their peptide ligands, we used the ligand docking program, AutoDock CrankPep (ADCP), to model interactions between these peptide ligands and the oxidized and reduced forms of the kinases. These studies suggest that oxidization of each kinase leads to subtle changes in the architecture of its ligand-binding sites that disrupt interactions with some ligands while not affecting others. Together, these studies offer important insights into the mechanisms of crosstalk between redox and phosphorylation-dependent signaling at the level of kinase substrate selection and have implications for kinase regulation during normal and pathological states.