Are LOBs also backed up if I take dump of all partitions of table individually? I am taking export of a large table in oracle through datapump. I am taking export of all partitions one by one. The table has a LOB column as well. Are LOBs also backed up with partitions? Because partitions seem to be very small as compared to LOBs
Yes, they should be. Unless, you have configured datapump to exclude them somehow. Please share the command (and parameter file) that you use to make the datapump export. 

Reasons why the dump file is smaller could be that you have large LOB indexes (which are not included, and should not be), or you are using compression.