Does the migration assistant transfer ioffice or do i have to buy it again?

It will transfer it but you will probably be asked to give again the serail number to reactivate it on the new Mac.

If you have reached the total number of possible activation according to your licence do not forget to deactivate the old one.

Thanks for the points niky911.

Usually the serial number is on the box of Office if you purchased it on DVD or in the mail you recieved after a purchase online and download.