$re = '/(?<=<strong>).*?(?=<\/strong>)/';
$str = '<table class=\'table table-condensed\'>
<tr>
<td>Monthly rent</td>
<td><strong>Fr. 1\'950. </strong></td>
</tr>
<tr>
<td>Rooms(s)</td>
<td><strong>3</strong></td>
</tr>
<tr>
<td>Surface</td>
<td><strong>93m2</strong></td>
</tr>
<tr>
<td>Date of Contract</td>
<td><strong>01.04.17</strong></td>
</tr>
</table>';
preg_match_all($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