Strap reinforcement is very commonly used as reinforcement material in mechanically stabilized earth walls (MSEW). Metal straps are mostly used as reinforcement material. However, in humid climates, where the risk of damage to metal straps due to corrosion is high, the use of geosynthetic straps is quite justified. In the Croatian coastal region, geosynthetic straps were used as reinforcement for two very high MSEWs. In both cases, the backfill material crushed stone aggregate from the neighboring site was used. According to the relevant standards, it is recommended that the backfill material should have a uniformity coefficient of Cu ≥ 4.0. To meet these requirements, it is usually necessary to sieve and crush the backfill material. To evaluate the influence of the uniformity coefficient on the friction interaction coefficient between a geosynthetic strap and a crushed stone aggregate, a series of pullout tests with different confining stresses and aggregate grain size distributions were conducted. The pullout tests were performed for three different uniformity coefficients of the crushed stone aggregate. The results confirmed the justification to use backfill material with a uniformity coefficient higher than 4.0. The pullout tests were performed with one strap, two closely spaced straps, and two separated straps. The results showed that lateral friction contributes to the pullout force in the amount of 16.1% of the total force.