We present a schedulable garbage collection for realtime applications in virtual machine environments. The design objective is to make the pause time caused by garbage collection operations controllable, and the invocation of garbage collection predictable. Thus, real-time applications can be schedulable along with garbage collection. We develop a prototype for a schedulable garbage collection in MONO CLI execution environment. A cost model of garbage collection is established based on measured WCET to predict the execution time and overhead of garbage collection operations. A scheduling algorithm of garbage collection and application tasks is presented to illustrate how the time and memory constraints of real-time systems can be met. The experiment result of the scheduling algorithm for a periodic task set on the prototype is included in the paper.