In this paper, we analyze the performance of a CDMA unslotted ALOHA system with burst reservation. A mobile terminal reserves the channel for the duration of its burst and transmits spread packets. The packets are transmitted in unslotted mode. As the packet transmission of the mobile terminal can be begun at any time, the level of multi-user interference fluctuates during the packet transmission. We, therefore, calculate the bit error probability and throughput by considering not only the number of overlapped packets but also the amount of time overlap. We assume that the generation of bursts is Poisson distributed, the number of packets transmitted at once by a mobile terminal is geometrically distributed, and the packet length is constant. By modeling the system as a Markov chain, we obtain the throughput of CDMA unslotted ALOHA system with burst reservation.