The magnetic field effect on the formation of a water droplet was investigated by measuring the volume of water droplets formed in a magnet with a vertical field distribution. The maximum field was 9 T at the center of the magnet bore. The droplet volume increased significantly on the upper side of the magnet with a strong field gradient and decreased at the lower side. Measurements were also carried out for several diamagnetic and paramagnetic aqueous liquids, and showed that the same effect was introduced by the presence of a magnetic force. The results agreed with those of calculation. We also succeeded in controlling the droplet volume under a magnetic field of below 1 T by forming a droplet of a liquid in another liquid of similar density.