The rapid advancement of wireless communication technology has had a significant impact on modern society, bringing about revolutionary changes in our daily lives and means of communication. In particular, introducing 5G and Beyond 5G (5G/B5G) networks is expected to expand communication coverage, including in the sky, at sea, and in outer space, while enabling ultra-low power consumption and low-cost communication. In order to adapt to such developments, Network Slicing (NS) is a technology that virtually divides the communication infrastructure to optimally allocate resources tailored to the requirements of individual services. Also, it is important to select slices that match the characteristics of each service. In B5G networks, individually optimized slices are required to support a wider variety of services and applications. To ensure that resources are distributed effectively without compromising the performance of any slice, in this paper, we propose a Fuzzy-based System for Selection of Slice Service Type (F3ST), which considers four parameters: Bandwidth (Bt), Latency (La), Connection Density (CD) and Slice Ability for Mobility Management (SAMM), which is a new parameter. From simulation results, we found that when Bt and SAMN are increased, the Slice Service Type Decision (SSTD) value is increased, but when La and CD are increased, the SSTD is decreased.