which is the world largrest book publishing house ?

Answer 1

These claim the title:

WW Norton and Company Oldest and largest publishing house owned wholly by its employees ...
www.wab.org/aln/alnweb/resources/publishers.html

The US Government Printing Office (the GPO) is the largest publishing house in the world.
www.morainevalley.edu/LRC/govdocs.htm

Random House, the largest publishing house in the world,
www.press.umich.edu/jep/04-03/lichtenberg.html

Devon Publishing Group, the largest publishing house in the world.
www.canadianartprints.com/artsubmis.html

Answer 2

I sure do not know that one. too many claim the honor. I would bet the US government is either the top or second.