How to Remove All Contacts From QuickBooks
Using the QuickBooks Customer Center, you can delete multiple contacts that were created within the QuickBooks program. If you need to delete contacts that you have synced with a third-party program such as Microsoft Outlook, you have to mark the contacts as inactive. While marking the customer as inactive doesn't delete it from your software, it does prevent the customer from appearing in the Customer list. You can delete each customer in the list individually, but you can't delete them all at once in QuickBooks.
Click the "Customers" menu and "Customer Center."
Select the "Customers & Jobs" tab.
Click on the first customer you want to remove and press "Control-D" or click on the "Edit" menu and "Delete Customer:Job." Continue to delete each customer you want to remove.
To make the customers inactive, click on the first customer and click the "Edit" menu. Choose "Select All." Click the "Edit" menu again and select "Mark as Inactive."
Information in this article applies to QuickBooks 2013. It may vary slightly or significantly with other versions or products.