A low-temperature fired ceramic circuit substrate fired at a temperature ranging between 800.degree. and 1,000.degree. C. includes a plurality of insulating layers each formed of a low-temperature fired ceramic, an Ag conductor layer formed internally of the substrate, an Au conductor layer formed on a surface of the substrate, and an Ag--Pd layer formed between the Ag and the Au conductor layers, the Ag--Pd layer being composed of 100 parts metal composition consisting of 70 to 95 parts Ag and 5 to 30 part Pd by weight, and 2 to 10 parts lead borosilicate glass by weight. As the result of the above composition of the ceramic circuit substrate, its fabrication process can be simplified, and a defect rate in a connection between the Ag and Au layers after repeated firing is rendered approximately zero, which ensures high reliability for the connection.