The present invention relates to a fluid agitator which may stir fluid in a closed space without leakage of the fluid. The fluid agitator has a motive means and a bearing means installed in the closed space. In the fluid agitator employing a electric motor as the motive means, only the stator coil of the motor which is weak in its resistance against high temperatures and humid atmosphere is sealed in a sealing chamber. The sealing chamber may be provided with a cooling device to cool the inside thereof. The driving shaft of the motor is supported by a bearing having resistance to high temperatures and high humidity and is provided with an agitating blade. In the fluid agitator employing a turbine system as the motive means, a turbine chamber and a turbine blade are set in the closed space. A fluid supply is furnished to introduce fluid into the turbine chamber from outside of the closed space for driving and rotating the turbine blade. The turbine blade is connected to an agitating blade through a rotation transmission.