$re = '/(?s)<Device(?:(?!<\/Device).)*<Block[^>]+Name="ZG123CZ123".*?<\/Device>/';
$str = '<Device DevID="14212111" Model="" GroupID="">
<Block Name="ZG123CZ123" LastFileDld="" LastFullDld="">
<Group ZD="1">
<DSize ParamName="KEY" Value="RAM"/>
<DSize ParamName="REM" Value="***"/>
<DSize ParamName="*UNZIP" Value="I:ZG123CZ123.ZIP"/>
</Group>
<Group ZD="15">
<DSize ParamName="REM" Value="="***""/>
<DSize ParamName="#DEBUGPORT" Value=""/>
</Group>
</Block>
<DevFiles />
</Device>
<Device DevID="14212111" Model="" GroupID="">
<Block Name="DG" LastFileDld="" LastFullDld="">
<Group ZD="3">
<DSize ParamName="*UNZIP" Value="DG.ZIP"/>
<DSize ParamName="*GO" Value="F:DG.OUT"/>
</Group>
<Group ZD="15">
<DSize ParamName="#LOGPORT" Value="NONE"/>
<DSize ParamName="CDH6" Value=""/>
</Group>
</Block>
<DevFiles />
</Device>
<Device DevID="14212111" Model="" GroupID="">
<Block Name="ZG123CZ123" LastFileDld="" LastFullDld="">
<Group ZD="1">
<DSize ParamName="KEY" Value="RAM"/>
<DSize ParamName="REM" Value="***"/>
<DSize ParamName="*UNZIP" Value="I:ZG123CZ123.ZIP"/>
</Group>
<Group ZD="15">
<DSize ParamName="REM" Value="="***""/>
<DSize ParamName="#DEBUGPORT" Value=""/>
</Group>
</Block>
<DevFiles />
</Device>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php