Hi @hasnainv,
What version of python and boto are you using?
Do you get any error back?
Do you have example code to recreate this issue?

Boto version is 2.34.0. Python version is 2.7.5

My code:

from boto import ec2
conn = ec2.connect_to_region(opts.region)
vols = conn.get_all_volumes(filters={'attachment.instance-id': instance_ids})

for volume in vols:
conn.delete_volume(volume.id)

I double check in the web interface that all the volumes in vols exist.
Here, conn.delete_volume(volume.id) throws no exception or error messages. It just doesn't delete the volume.