Retrieve the associated annotation from Uniprot
You can upload your list of accession numbers to the batch retrieval service for the UniProt Konwledgebase, http://www.uniprot.org/uploadlists

A video tutorial for this service is available at https://www.youtube.com/watch?v=kLdgjqWoMZc

Once you have retrieved your proteins, you can click on "Columns" to customize your output and add columns, e.g. for function annotation. See also http://www.uniprot.org/help/customize or http://insideuniprot.blogspot.ch/2015_03_01_archive.html 
Results can then be downloaded in tab-separated format.

If you have any additional questions, please don't hesitate to contact the UniProt helpdesk.