There are 2 ways to add a new tab to the product edit page in admin panel of Magento.

First method:
Let’s add a tab for a custom module.
Add the following code to your config.xml file in the global scope:

<blocks>
...
    <modulename>
        <class>Company_ModuleName_Block</class>
    </modulename>
    <adminhtml>
        <rewrite>
             <catalog_product_edit_tabs>Company_ModuleName_Block_Adminhtml_Tabs</catalog_product_edit_tabs>
         </rewrite>
     </adminhtml>
...
</blocks>

After this you should create a new file: Company/ModuleName/Block/Adminhtml/Tabs.php The content of this file you can see below

<?php

class Company_ModuleName_Block_Adminhtml_Tabs extends Mage_Adminhtml_Block_Catalog_Product_Edit_Tabs
{
    private $parent;

    protected function _prepareLayout()
    {
        //get all existing tabs
        $this->parent = parent::_prepareLayout();
        //add new tab
        $this->addTab('tabid', array(
                     'label'     => Mage::helper('catalog')->__('New Tab'),
                     'content'   => $this->getLayout()
             ->createBlock('modulename/adminhtml_tabs_tabid')->toHtml(),
        ));
        return $this->parent;
    }
}

The code above rewrites the system function which generates the layout and adds the tab.

Next, you need to create a file: Company/ModuleName/Block/Adminhtml/Tabs/Tabid.php

<?php

class Company_ModuleName_Block_Adminhtml_Tabs_Tabid extends Mage_Adminhtml_Block_Widget
{
    public function __construct()
    {
        parent::__construct();
        $this->setTemplate('modulename/newtab.phtml');
    }
}

Note: template should be in app/design/adminhtml/…/…/template/

Second method:

Simply copy the file app/code/core/Mage/Adminhtml/Block/Catalog/Product/Edit/Tabs.php to a local folder (app/code/local/Mage/Adminhtml/Block/Catalog/Product/Edit/Tabs.php) and add the following snippet to the function _prepareLayout()

$this->addTab('tabid', array(
              'label'     => Mage::helper('catalog')->__('New Tab'),
              'content'   => $this->_translateHtml($this->getLayout()
     ->createBlock('modulname/adminhtml_tabs_tabid')->toHtml()),
));

After this, simply follow the instructions above.

We hope this article was helpful. Comments are welcome.