Provided is a system for sampling and pretreating biological fluid. It comprises: a piercing unit having at a lower portion a capillary tip which is to be inserted into skin to a predetermined depth to take biological fluid therethrough; a dropper, connected to an upper portion of the piercing unit, having an injection tube at an upper portion thereof, the injection tube communicating with the capillary tip; and a reagent container, designed to accommodate the piercing unit therein in an airtight manner so as to seal an outer circumference of the piercing unit, functioning to contain a reagent for treating the biological fluid of the capillary tip of the piercing unit. The system allows even a novice to sample and pretreat biological fluid with high accuracy without the use of expensive precision devices. The system employs fewer expendable supplies, thus providing higher convenience for the user.