Risk has become part of human life, such as workers who face risks that originate from their jobs. The rise of the existing development in the city of Yogyakarta makes Occupational Health and Safety a problem that has attracted much public attention. The purpose of this study was to analyze K3 risk and how to assess OHS risk in the lecture building project activities. Risk assessment is a process for analyzing risks and evaluating risks before continuing to do work. From the data obtained, there are 16 activity variables that have high risk classification values including the work on land excavation of workers affected by landslides, when moving service crane material to hit workers, and when moving material to workers overwritten material, at foundation work at the time drilling drilling tools crashing into workers or facilities, and at the time of making the guide wall workers fall into the excavation, at work Hot work workers are exposed to welding sparks, and can cause fires if the tube leaks, at work casting workers fall from heights, on column work the beam workers fell from a height, and workers were crushed by objects on top of it, on the job of installing scaffholding workers fell from a height, and workers were struck by falling objects, in the work of lifting material with tower cranes material fell and hit workers, on roof work height, in plumbing work workers are subjected to electric shock. That's the work that must be considered because it can endanger the workers of multi-storey building projects.