In the present study, an attempt was made to establish a relationship between geogrid aperture size and aggregate particle size required for a good interlocking between them. A simple and predictive test called "aggregate column test" was performed for this aim. In this test, an aggregate column with a dimension of 40x40x60 cm (width x length x height) reinforced with geogrid layers is formed and vertically loaded to a certain degree. Three types of aggregate and a biaxial extruded polypropylene geogrid were used in the tests. A series of tests were performed with different geogrid intervals (vertical spacing) ranging from 60 to 7.5 cm. If the aggregate column does not collapse and can carry a vertical load up to a certain degree, it means that there is a good interlocking between the geogrid and the aggregate. On the other hand, if the aggregate column cannot bear the intended vertical load or collapses even under its own weight, it means that there is no interlocking between the geogrid and the aggregate. This concept constitutes the basic philosophy of this experiment. The ratio of nominal aperture size of the geogrid (d(A)) and predominant particle size of the aggregate (d(90)) was taken into consideration for interlocking. Besides, the ratio of nominal aperture size of the geogrid (d(A)) and mean particle size of the aggregate (d(50)) was also considered. As a result, d(A)/d(90) ratio was found as 1.3 and d(A)/d(50) ratio was found as 2.1 for the best interlocking.