To obtain magnetic fluid excellent in dispersion, fluidity and endurance, by making the fluid contain silicone oil, carboxyl group containing anion based surface-active agent, and magnetic metal oxide particles and/or magnetic metal particles.

The title magnetic fluid of silicone oil base contains silicone oil, carboxyl group containing anion based surface-active agent, and magnetic metal oxide particles and/or magnetic metal particles. The magnetic fluid is manufactured as follows. Alkaline suspension is obtained by adding alkaline agent to suspension liquid dispersing magnetic metal oxide particles and/or magnetic metal particles; carboxyl group containing anion based surface active agent to the alkaline suspension; pH of the suspension obtained in the above is prepared to be at most 2; the obtained acid suspension liquid is dried; and the dried object and silicone oil are mixed. Thereby magnetic fluid of low vapor pressure which is applicable to a wide temperature range, non-toxic and safe can be obtained.