<ul>
<?php
foreach((get_the_category()) as $category) {
$cat_id=$category->cat_ID . ' ';
}
$myposts = get_posts("numberposts=50&category=".$cat_id."&orderby=post_modified");
foreach($myposts as $post) : ?>
<li><?php echo date("Y.n.j", strtotime($post->post_modified)); ?> : <a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a> </li>
<?php endforeach; ?>
</ul>
