In this paper, we propose a new filesystem named Ad-hoc Filesystem which targets ad-hoc wireless networks. Ad-hoc Filesystem is a serverless filesystem which automatically generates temporary shared space among multiple mobile machines when they gather in a communicable range. The generated space is kept stable as long as possible even if some machines join or leave the communicable range. We have designed an initial prototype of Ad-hoc Filesystem and have conducted preliminary evaluations on the simulator. Our design is strongly based on an assumption such that people who wish to work together would form a stable group with a single mobility behavior. Based on the assumption, our prototype distributes files among multiple machines and duplicates each on two machines, then it keeps the pairs of such machines as long as possible. We also introduced another strategy to increase file availability by exploiting each machine’s client cache. The simulation results show that controlling packets used in our prototype to maintain system state hardly affects the overall system performance. Also the result indicates that our strategy that keeps two replicas for each data and exploits client caching is effective to achieve high availability.