Reinforcement by fibers is one of the most practical and economic methods to improve some engineering properties and the mechanical behavior of soils in civil engineering. In this paper, the impact of fiber reinforcement on the swelling behavior of bentonite clay was investigated. Virgin homopolymer polypropylene (HPP) and copolymer polypropylene (CPP) with various percentages were used as reinforcement materials, and the influence of fiber contents on one-dimensional swelling pressure was evaluated. At first, sieve and hydrometer analysis and Atterberg limits tests were conducted on bentonite. The standard Proctor compaction test was also used to determine the compaction properties of reinforced and unreinforced bentonite. Then, the oedometer test was carried out on specimens. The results showed that both types of fiber enhanced the swelling potential of bentonite. The optimum amount of fibers was analyzed via test results. Moreover, the most significant improvement in terms of reducing the swelling potential of bentonite was observed due to the use of HPP fiber. The maximum improvement percentages to reduce the swelling pressure of bentonite layers using HPP and CPP fibers were 44.2% and 29.4%, respectively. The statistical analysis was carried out to identify the relationship between the dependent variables (fiber-reinforced samples) and the independent variable (plain bentonite). The result indicated the proper agreement of the model and concerning values. Two significant equations were calculated to estimate the swelling pressure of bentonite with HPP and CPP fibers that showed the use of synthetic fibers additives has a considerable effect on decreasing the swelling pressure of expansive soils.