Wearable biosensors are nowadays a critical filed of research in many fields of research such as sweat sensors that closely monitors useful biomarkers from the non-invasive body fluids such as sweat, urine, blood, and saliva, and tears. - Sweat is a primarily accessible body fluid that contains measurable analytes such as lactate, glucose, ethanol, and ammonia. - Other than biological molecules, physical measurements also provided useful health information such as body temperature, heartbeat pulse, and skin conductance. These intrinsic applications make wearable sensors integrated with novel nanomaterials on flexible substrates promising for smart health monitoring devices. - However, current electrical wearable detection of lactate can be limited by its low sensitivity, poor stability, requirement of external power sources, sophisticated fabrications, and high cost. - Hence, it is imperative to develop new strategies to fabricate cost-effective wearables. in this work, we presented a new inkjet printable reduced graphene oxide (rGO) ink method to fabricate a low-cost chemiresistive biosensor for lactate detection from sweat matrix with high sensitivity and selectivity, via inkjet printing of the rGO ink followed by optimized functionalizations. The sensor demonstrated a high response at 0.49 per µM and low LOD at 23 µM.