You can import MBOX to Gmail with Thunderbird email client. First of all, import MBOX files into Thunderbird. Now, configure your Gmail account with Thunderbird and then move MBOX files into Gmail mailbox folder. Hence, you can manually upload MBOX file into Gmail. However, if want a quick solution try Advik MBOX Converter tool on your system. It preserves data integrity and folder hierarchy during the importing process. It is a stand alone utility. It supports all latest and old versions of Windows OS. The software provides various advanced filter options to import selected emails based on date range, Sender, Recipient, etc. Download the software and try for free.