Hi Srikanth,
If you need master data process chains to run them on monthly basis, then Go to start variant of process chain and check for Scheduled Check box and click on Edit Conditions option,
And then you can specify your conditions --> click on Date/Time Button and give relevant scheduled date and time.
Then click on Period values to specify your periodic condition.
Please go through link http://scn.sap.com/thread/1191872 for more details.
Thanks,
Mukta