Over the last few years, real-time CORBA are increasingly used in development of distributed real-time applications, in which real-time CORBA and operating system constitute the computing and communication infrastructure upon which the applications execute. However the amount of effort put into studying and evaluating the real-time characteristics of real-time CORBA is still inadequate. In this paper we focus on examining the overhead and predictability of real-time CORBA, which are two of the most important concerns when building real-time applications. Firstly we introduce the desired features in real-time applications and possible sources of unpredictability. Secondly, we evaluate a real-time CORBA implementation : TAO v1.2 on Linux kernel v2.4.18 over 100M Ethernet. It is observed that: 1) the overhead of TAO is acceptable, compared with the equivalent application using TCP/IP socket directly; 2) TAO presents rather predictable behaviors under light network traffic, but unpredictability of CORBA invocations increases significantly as the network becomes overloaded. Moreover, we identify that the major source of unpredictability of CORBA invocations is in the TCP/IP stack of Linux rather than in TAO itself.