Obesity is a prevalent metabolic disorder linked to insulin resistance, hyperglycemia, increased adiposity, chronic inflammation, and cognitive dysfunction. Recent research has focused on developing therapeutic strategies to mitigate cognitive impairment associated with obesity. Insulin growth factor-1 (IGF1) deficiency is linked to insulin resistance, glucose intolerance, and the progression of obesity-related central nervous system (CNS) disorders. In this study, we investigated the neuroprotective effects of IGF1 in two obesity models: diet-induced obesity (high-fat diet mice) and genetic obesity ( ob/ob mice which is genetically deficient in leptin), and in vitro Neuro2A neuronal cells and primary cortical neurons under insulin resistance conditions. We performed RNA sequencing analysis using the cortex of high-fat diet mice injected with IGF1. Also, we detected cytokine levels in blood of high-fat diet mice injected with IGF1. In addition, we conducted the Barnes maze test as a spatial memory function test and open field test as an anxiety behavior test in ob/ob mice. We measured the levels of proteins and mRNAs related to insulin signaling, including synaptic density proteins in brain cortex of ob/ob mice. Our results showed that IGF1 injection enhanced spatial memory function and synaptic plasticity in obese mice. Furthermore, in vitro data demonstrated that IGF1 treated neurons revealed enhanced neural complexity and improved neurite outgrowth under insulin resistance condition through the AKT-GSK3β-BDNF pathway related to antidepressant, cognitive function and anti-apoptotic mechanisms. Therefore, our results provided that IGF1 have potential to alleviate cognitive impairment by promoting synaptic plasticity and neural complexity in the obese brain.