You can't import metadata from HTML files*, it must be XML. See [Import Metadata (Conversion)][1].

> - Text or HTML files containing metadata can't be imported. 

*If the HTML was generated by the [USGS `mp` tool][2] it may be possible to convert it to text and then to XML with mp. For more information see [Importing metadata][3].


  [1]: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Import_Metadata/00120000000w000000/
  [2]: http://geology.usgs.gov/tools/metadata/
  [3]: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Importing_metadata/00120000004q000000/