The organ in the body responsible for filtering blood is the kidneys. These paired organs are located on either side of the spine in the lower back. The kidneys perform vital functions, including filtering waste products and excess substances from the bloodstream, regulating electrolyte levels, and maintaining fluid balance. They produce urine, which is excreted through the urinary tract. The health of the kidneys is crucial for overall wellbeing, and their failure can lead to serious health complications.