The present invention provides a process for producing a wiring circuit board which can be inhibited from developing whiskers and can be reduced in the unevenness of connectivity with electronic parts while retaining the connectivity. According to the present invention, a wiring pattern 12 comprising a thin metal film 31 and a conductor layer 33 is formed on a base insulating layer BIL. A tin-plated layer 34 is formed by electroless plating so as to coat the wiring pattern 12 therewith. The wiring pattern 12 and the tin-plated layer 34 are then subjected to a heat treatment. The heat treatment temperature and heat treatment period are regulated to 175 to 225.degree. C. and 2 to 10 minutes, respectively. By the heat treatment, a mixture layer 35 comprising copper and tin is formed. Thereafter, a solder resist SOL is formed over the base insulating layer so as to cover the wiring pattern 12 and tin-plated layer 34 in given regions. Subsequently, the solder resist SOL is subjected to a heat curing treatment.