The Common Object Request Broker Architecture standardizes a platform- and programming-language-independent distributed object com-puting environment. It also provides a standard for several distributed servic-es. The Object Transaction Service provides an object-oriented framework for distributed transaction processing, especially for Online Transaction Pro-cessing in business applications. The current CORBA OTS allows multi-threading inside a transaction, leaving, however, thread coordination to the application programmer, which can be dangerous. Based on the Open Multi-threaded Transaction model, we present in this paper the design of a Thread Synchronization Coordinator, ThreadSyncCoordinator, which provides the desired thread control inside a multithreaded transaction. A blocking commit protocol ensures that once in a transaction, a thread cannot leave before the outcome of the transaction has been determined, guaranteeing the ACID properties for multithreaded transactions. We also show how the Thread-SyncCoordinator can be used to design and implement complex applications, e.g., an Online Auction System, in an elegant way.