How to set HTML value for taxonomy description field using entity_metadata_wrapper
I just encountered a similar situation myself and it looks like you're choices are either taxonomy_term_save() or to update the table directly via  db_update(). The format property belongs to the term itself, rather than the Description property of the term. If you execute $term-&gt;getPropertyInfo() you'll see that the format property is not returned. Keep in mind that the Description is a property of the taxonomy entity, rather than a field, but doesn't seem to be accessible via EMW.

taxonomy_term_save()

taxonomy_term_save((object)array(
  'tid' =&gt; $tid,
  'description' =&gt; $t($descriptions[$info['step']]),
  'format' =&gt; 'full_html',
  'vid' =&gt; $vocab-&gt;vid,
));