Ferrofluidic robots with excellent deformability and controllability have been intensively studied recently. However, most of these studies are in vitro, the use of ferrofluids for in vivo medicinal applications remains a big challenge. The application of ferrofluidic robots to the body requires the solution of many key problems. In this study, the biocompatibility, controllability, and tumor-killing efficacy were considered when creating a ferrofluid-based millirobot for in vivo tumor-targeted therapy. For biocompatibility problems, we used corn oil specifically for the ferrofluid robot. In addition, we built a control system that enables a three-dimensional magnetic drive to be implemented in complex biological media. Using the photothermal conversion property of 1,064 nm, ferrofluid robot can kill tumor cells in vitro; and inhibit tumor volume, destroy the tumor interstitium, increase tumor cell apoptosis, and inhibit tumor cell proliferation in vivo. This study provides a reference for ferrofluid-based millirobots to achieve targeted therapies in vivo. This article is protected by copyright. All rights reserved.