Abstract: This is a summary report for the 4th International Forum on Opto-electronic Sensor-based Monitoring in Geo-engineering(4th OSMG-2012).This forum was sponsored by Nanjing University, organized by Nanjing University High-tech Institute at Suzhou, and supported by National Science Foundation of China(NSFC) and other organizations. The forum shows the following four features in the recent years: (1)Theoretical researches have been enhanced and a series of fundamental research output have emerged.(2)More and more innovative sensors tailored for geo-engineering monitoring have been developed recently, which show unique benefits regarding accuracy, stability, reliability and integration ability.(3)the applications of distributed sensing technologies in safety monitoring of geo-hazards and geotechnical structures have been advocated extensively. Some monitoring systems have been established for specific projects.(4)the fully-distributed and qusai-distributed fiber optic sensing technologies have been introduced into the disciplines of hydraulic, transportation, fire protection, electric power, and national defense engineering. Standardization has been widely concerned. The future researches may focus on the following four aspects: (1)development of cost-effective demodulation techniques for fully-distributed fiber optic sensing technology; (2)development of special fiber optic sensors for geo-engineering and their field installation methods; (3)transmission and processing technologies of huge monitoring data from distributed fiber optic sensors; (4)early warning and stability assessment methods for geo-hazards and geotechnical structures based on distributed monitoring technologies.