Nonmagnetic colloids, polystyrene latex particles in electrolyte solutions, are exposed to a magnetic field of low flux density, and effects of the magnetic exposure on their zeta potential and diffusivity are investigated, measuring the mobility by microelectrophoresis and the diffusivity by photon correlation spectroscopy. The results are compared with the magnetic effects on the coagulation rate reported previously. It is found that (1) the magnetic exposure reduces the zeta potential and diffusivity of colloids, (2) the magnetic effect remains for at least 6 days, (3) the magnetic effect is attributable mainly to the particles rather than the bulk solution, and (4) the magnetic effects on the zeta potential are very similar to those on the coagulation rate. A possible mechanism to explain these results is proposed.