The utilization of well logging in the in-situ dotermination of ore bed grade is expected to be a research field with broad prospects, especially in places where coring is difficult to conduct. Techniques corrently used in China for grade determination by means of well logging can be grouped into two types. i. e. nuclear log and regression analysis. The former technique has been used to determine fluorite grade with the help of neutron-activation log, and the latter technuique has been applied to the glauberite and uraniferous phophorite exploration by using gamma-ray log.Both techniques have been carried out with success,and, as a result, a set of effective working procedures have been summarized.The determination of ore bed grade by means of well logging proves to be superior to the conventional method which basically consists of drilling and coring, visaal sampling and core assay. The edvantages of well logging lie in the following aspects: it conducts continuous measurement to obtain complete information on ore beds; the detedion radius of well logging can be much larger than that of coring; well logging can get rid of the errrors that exist in chemical analysis due to poor core recovery and random sampling. Therefore,well logging yields more reliable data for grade determination, as is clearly demonstrated by practical examples of three ore districts in China. Well logging may serve as a guide for reasonble sampliny and can be used effusively to work cot a program for further exploration. When core recovery is low or when certain ore beds are not intersected by drilling,well logging can be used. The result obtained by well logging is are the same as that obtained by core analysis because they are two different techiques that work independently,using different sampling methods and determine differeknt types of samples. Thus, the credibility of grade determination depends not only on measurement accuracy, but also on the actual grade of ore bed that the determination by each technique can represent, which suggests that the result of core assay can not be regarded as the only standard for grade of ore beds.