Abstract: Weathered rock mass often contain weak zones. The weak zones reduce the mechanical strength of rock mass substantially.To locate and describe the weak zones,drillholes are employed to take rock samples. But,because of reason of economic and construction period,the number of drillholes is limited and the weak zones cannot be located accurately and efficiently. This causes problems in accurately analyzing mechanical properties of rock mass. This kind of problems can induce instability of rock mass in slopes and foundations. This paper introduces a new method to detect and characterize weak zones in weathered rock mass. This method applies Drilling Process Monitoring system(DPM)to monitor the full drilling processes for installation of soil nails,tiebacks,anti-slide piles and so on. Without taking samples,the weak zones can be detected and characterized with the analysis of DPMdata. The case study shows that this method can efficiently and quickly detect and characterize the weak zones in weathered rock mass. This method can be useful to better investigate weathered rock mass for design and construction.