Geosynthetic reinforced soil retaining walls (GRS RWs) technology has been spread worldwide mainly due to higher seismic stability of this type of structures compared to the conventional unreinforced backfill retaining walls. GRS RWs typically use geogrids as backfill reinforcement material. In the present research, a new type of tensile reinforcement comprising of square shaped geocell is presented. A mattress of square shaped geocell is constituted by interconnected st raight longitudinal and transversal members which are able to accommodate and confine larger soil particles within its cells unlike planar geogrids. In order to investigate the effects of the cell size of a geocell mattress on the overall pullout resistanc e of this material embedded in gravelly soils, a series of pullout tests were conducted. There is a value of S, 60 mm, leading to maximum peak pullout resistance and initial stiffness, when S of the geocell buried in Gravel No.1 increases. But when the geo cell was buried in Gravel No.3, there is not such a value. The peak pullout resistance is increased when H T increases. When D 50 increases from 3.2 mm (Gravel No.1) to 7.5 mm (Gravel No.3), there is no significant effects on the peak pullout resistance .