Abstract: Kostanjek landslide in Zagreb has been active since 1963. The engineering geological model of landslide Kostanjek is interpreted on the basis of geotechnical investigations from the period 1988-1989, and based on doctoral research for the PhD thesis that was released in 1996. (Ortolan, 1996). Based on this engineering geological model, a landslide remediation meassures were designed in 2008th, its performance was so far sustained primarily due to the high cost of construction. This landslide is chosen as a pilot area of bilateral Croatian-Japanese SATREPS FY2008 project because its high level of risk due to the reactivation of landslide Kostanjek .Within the framework of scientific research activities in 2011 a system for landslide monitoring was established. In addition, since 2010 additional research was conducted in order to collect new data for reinterpretation of the landslide engineering geological model. Summarized in this work are the engineering geological conditions and historical information about the research and interpretation of landslide Kostanjek. Based on data from literature and historical documentation, a systematization of the existing data of the sliding surfaces that are registered in wells and boreholes and on faces of cuts in open pit mines is made. New input data for modeling the landslide are also collected so as determination and description of the core from the new borehole B-1, 100 m in depth, for purposes of comparing it with the previously interpreted stratigraphic profile in the central part of the landslide, inclinometer measurements to determine the sliding surface in the central part of the landslide, the collection of data of groundwater levels in wells at the area o landslide and in its vicinity, and water sampling for chemical analysis. At the end of the thesis a review of the comparability of historical and new data is given, as well as the usability of the new data collected in the reinterpretation of the geological engineering model of the Kostanjek landslide.