We have measured the spreading areas of seven commercial soldering fluxes and silver solder on 18% Cr-8% Ni stainless steel plates at 750℃, 800℃ in air.We have also tested the tensile strengths of the joints of the same steel bars bonded with the same fluxes and solder and calculated the soldered area fractions of the total cross-section of the soldered bars.Significant differences were found between these seven fluxes in the spreading of the flux and the solder, the joint strength, and the soldered area fraction(p<0.01).The spreading of the solder did not necessarily increase with the increased spreading of the flux.The flux which enhanced the spreading of the solder had a tendency to increase the joint strength and the soldered area fraction.These find suggested that each of the fluxes were different in surface tension, viscosity, ability of dissolving the oxides and lowering of the surface tension of the melted solders.We concluded that the fluxes tested were acceptable clinically because of adequate joint strengths.