You can upload your list of UniProtKB 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
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.