The present invention relates to an electroless gold plating solution, and more particularly, to a gold plating solution low in toxicity and stable for a long time. 
Hitherto, an electroless gold plating solution has been known which contains gold(I) potassium cyanide, potassium cyanide and a borane compound as main constituents, as disclosed in Plating, 57 (1970), pp.  914-920.  By using the plating solution, a plating rate of 1 .mu.m/hr and stability of the solution are ensured.  However, since the plating solution contains a large amount of cyanide ions, there is a safety problem in operation with the solution and in disposal of a waste liquid. 
As electroless gold plating solution not containing cyanide ions, a gold plating solution containing gold(III) chloride and hydrazine as main constituents is disclosed in U.S. Pat.  No.  3300328, and a gold plating solution containing gold(III) potassium chloride and a borane compound is disclosed in Japanese Patent Publication No.  56-20353 (1981).  However, since both of the electroless gold plating solutions disclosed respectively in U.S. Pat.  No.  3300328 and Japanese Patent Publication No.  56-20353 (1981) contain gold ions in the gold complex in the state of trivalent gold ions, the use of the solutions requires a larger amount of reducing agent, as compared to the case of using gold(I) potassium cyanide.  In addition, the electroless gold plating solution disclosed in U.S. Pat.  No.  3300328 is so unstable that precipitation occurs in the plating solution in about 2 hours, making it impossible to continue plating.