We investigate the effects of introducing a defect layer in a one-dimensional photonic crystal containing single negative material layers on the transmission properties.The width of the defect layer js taken to be the same or smaller than the period of the structure.Different cases of the defect layer being linear or nonlinear and double positive or double negative are discussed.It is found that only a nonlinear double negative layer givas rises to a localized mode within the zero-φeff gap in this kind of structure.It is also shown that the important characteristics of the nonlinear defect mode such as its frequency,its FWHM and the threshold of the associated bistability can be controlled by changing the widths of the defect layer and the host layers.