The transport of charge carriers in conducting layers generate excess low frequency noise which is 1/fatype. The main problem is if 1/f fluctuation is caused by fluctuation of number of carriers acting in transport or by mobility fluctuation due to scattering process. The objective of our research consisted in finding a correlation between the noise spectral density and nonlinearity on one hand and device time stability and reliability on the other. The noise of thick film resistor pastes 2041 and 8039 (10 k&OHgr;/sq.) was measured on resistors dimensions of0.3×0.3&hthinsp;mmand1×1&hthinsp;mm.The resistors were terminated by Ag/Pd and Ag conductors. Experimentally was observed, that noise spectral density is inversely proportional to the square of the sample length. ©1999 American Institute of Physics.