The photographic emulsions, which consist of suspensions of silver iodobromide nanoparticles in fish gelatin, were made by a double-jet method. The average sizes of the particles obtained by XRD measurement and TEM observation were 16 nm and 14.3 nm, respectively. The microwave photoconductivity measurement showed two first-order kinetic processes. The electron lifetime in the first process shortened obviously, indicating a mass of shallow traps on the nanoparticle surfaces. The second process was a slower decay one, which was considered as electron trapping followed by the reaction of trapped electrons with interstitial silver ions. A higher maximum frequency obtained in the dielectric loss measurement indicated formation of interstitial silver ions with high concentration on the surfaces of the nanoparticles. For sulfur sensitized nanoparticle emulsion, sensitivity and gamma increased with increase of both amount of sulfur sensitizer and sensitizing time, but the excessive amount of sulfur sensitizer rapidly led to the occurrence of additive fog density. In the case of the optimum sensitivity and gamma, sulfur sensitization centers, i.e., dimers of Ag₂S on the AgBr/I nanoparticle surface can be roughly estimated as no more than 500. The addition of methionine (Met) and methionine sulfoxide (Metsox) in the emulsion at chemical ripening made the density—(log exposure) curves shifted to lower exposure which demonstrated that their effective sensitization attributed to the bromine acceptance and to reducing the power of these additives.