Magnetic-controlled micro-robots have promising applications in disease therapy due to their high targetability and drug utilization. Due to their unique deformable and divisible properties, ferrofluid robots have gained much attention in microchemical reaction chips and micromanipulation. This letter proposes a biocompatible ferrofluid robot and validates its potential to achieve targeted drug delivery and tumor cell killing. This biocompatible ferrofluidic robot contains 10 nm oleic acid-coated ferric tetroxide particles and vegetable oil and has good magnetic responsiveness, deformability, and photothermal properties, and can move in liquid environments such as blood. It can achieve motion with an error of less than 0.4 mm under closed-loop control and obstacle overturning and passage through narrow channels less than twice its diameter. In addition, the biocompatible ferrofluid robot can kill tumor cells in the target area due to the photothermal properties of the magnetic particles, and experimental results show that the tumor cell death rate can reach 95%. These capabilities give the biocompatible ferrofluid robot a significant advantage in getting the target location for cancer treatment through the vascular environment.