A new natural gas pipeline with a 0.90-m diameter is under construction to provide a gas connection between Turkey and Greece as well as to create a gas ring for southern Europe. The new pipeline route lies next to an existing small diameter gas pipeline broken by a landslide that occurred in February 2006 near Karacabey (Bursa). Although the existing pipeline has been temporarily repaired, either the pipeline route should be relocated or the landslide should be stabilized. The geological survey conducted in the study area reveals that relocation is not feasible due to the existence of other landslides in close vicinity to the site. In order to investigate the causes of the landslide and to suggest possible remedial measures, geotechnical investigations including surface geological mapping, trial pitting, drilling with field tests, inclinometer measurements, laboratory testing, and limit equilibrium analyses were conducted. The investigation revealed that the unconsolidated clayey soil slid on claystone along a non-circular failure surface. Based on the gathered data, possible remedial measures including partial removal of landslide material and construction of toe buttresses, slope flattening, lowering the pipeline, and surface drainage systems were evaluated. These are suggested to prevent the reactivation of the landslide, and thus to establish a safe route for both the existing and the new pipelines.