The discontinuities play an important role in both the design and development stages of many geotechnical engineering projects. Therefore, semi-automatic detection of discontinuities based on remote sensing will save a considerable amount of time and cost. Accuracy of the semi-automatically detected discontinuities is also as important as the detection process, since the results directly reflect the uncertainty in the geotechnical problem. The current paper presents an accuracy assessment methodology for semi-automatically detected discontinuities from remotely sensed images. Semi-automatic lineament analysis is performed by using high-resolution satellite imagery for identification of rock discontinuities at the Andesite quarry area in Golbas1 Ankara, Turkey. A highresolution data IKONOS Precision Plus with 1m resolution orthorectified image has been used in the present study. The accuracy assessment methodology is developed based on a comparison of manually extracted lineaments using directional filtering and semi-automatically detected lineaments with LINE module of PCI Geomatica 8.2 and manual intervention. The proposed accuracy assessment methodology considers the accuracy based on location and length of the lineaments. In this respect, it has two dimensions. For the algorithm of the developed methodology, a software called LINECOMP, is coded in Java environment. The LINECOMP is composed of three modules. These are: LINE ADDRESS for identification of pixel addresses of lineaments; which is used for locational accuracy assessment; LINE COMPARE for comparing two lineament maps with respect to lineament pixels, which is used for length-based accuracy; and LINE CLASSIFICATION for classifying the assessed accuracy with respect to the amount of location and length matching. The performance of the proposed accuracy assessment method is also verified by the field studies carried out in the study area.