Wireless communication is characterized by constrained bandwidth, small coverage, short connection cycle, and subject to noise and disruption. Due to these characteristics, handling transactions requests from wireless mobile devices to a multi-level secure database requires special protocol to achieve efficiency and ensure security. In this paper we propose an advanced transaction scheduling protocol to address the database security and efficiency challenges in databases accessed over wired and wireless networks. The proposed protocol, called Priority/MLS/AL, is part of a complete framework which supports three priority levels for users and four security levels for data objects. The protocol assumes also that the transaction requests are initiated from different types of mobile stations, including cellular phones, personal digital assistants, laptops and personal computers. The extensive set of carried experiments shows evidently that the proposed scheduling protocol improves greatly the efficiency of the system, without breaching the security of the database.