Background: The adequate preload was the goal of hemodynamic optimization for sepsis resuscitation. The fluid strategy in the early phase of sepsis is unclear. Objective: To investigate the efficacy of a fluid bolus to prevent new-onset hypotension in suspected sepsis patients with hyperlactatemia (Point-of-care serum lactate 2-4 mmol/L). Methods: The Fluid Bolus in Suspected Sepsis Patients with Hyperlactatemia Trial (FISH) is a single-center, open-label randomized controlled trial. Participants will be patients suspected of having sepsis with hyperlactatemia (Point-of-care serum lactate 2-4 mmol/L) in the emergency department of Srinagarind Hospital, Thailand. Eligible patients will be randomized (1:1) to one of the study arms using block randomization. They will be placed in either the fluid bolus group (intervention, 30 mL/kg within 3 hours) or the standard care group (control). The primary outcome is new-onset hypotension within 24 hours after randomization. Secondary outcomes include lactate clearance, ∆SOFA at 72-hours, organ failure, and support ‘free days’ to day 28, 28-day mortality. Hypothesis: We hypothesize that a fluid bolus will prevent new-onset hypotension in suspected sepsis patients with hyperlactatemia (point-of-care serum lactate 2-4 mmol/L). Discussion: The optimal strategy for intravenous fluid therapy in a patient suspected of sepsis with hyperlactatemia is unknown. This is the first randomized trial examining fluid strategy in the early phase of sepsis with mild hyperlactatemia. Trial registration: TCTR20230502003