Abstract: Defective sewer pipes allow water and soil in the vicinity to drain into the pipe through defects. This eventually leads to sinkhole accidents. Such accidents have been reported around the world and cause economic losses and present a threat to human life. Many factors affect the state of soil erosion around defective sewer pipes, leak size is one of the most important of these factors. The present study studied the effects of leak width on soil erosion using local sandy soil and subbase type (D) which is a sewer pipe embedment material according to Iraqi specifications. Model tests were conducted with different leak widths of the following measurements: 3-7 mm where the experimental model involved soil exposed to cyclic water flow through leaks located at the bottom of the model. Eroded soil is collected, dried, weighted and sieved for each cycle. From the results, it was found that the leak width as well as the soil particle size both have significant effects on the amount of soil discharging into the sewer pipe where the amount of soil entering the sewer pipe through the leak is inversely proportional to the ratio of soil particle size to leak width.