The German motor-parts maker has decided to shift work to its factory in Hungary because the labour costs there are only 65 per cent of those in Wales, a company official said.
The Unite union called the development a "terrible blow" and a "bitter disappointment."
Bosch said the closure decision was prompted by the ongoing economic slump that saw a drastic 45 per cent drop in demand for alternators of high-end vehicles that the Miskin plant near Cardiff built.
Apart from the recession, another reason for the low demand has been a gradual shift in the market toward smaller, more fuel-efficient and less polluting vehicles.
Stefan Asenkerschbaumer, the president of the Bosch's starter motors and generators division deeply regretted that the company could not find a solution for the Cardiff plant.
Bosch in a statement yesterday said that it currently facing the worst economic crisis for many decades and has been especially hit in the automotive sector.
This April, the German multinational is set to announce its first operating loss in sixty years.