The diode laser brazing of heat-resistant alloys with precious filler metals has been conducted using tandem beam which consisted of preheating beam and main brazing beam. The 1mm thick Inconel 600 and A286 alloys were laser-brazed with the 0.5mm diameter Au-18%Ni, Ag-10%Pd and Ag-21%Cu-25%Pd filler metals using a brazing flux. The processing parameters of laser power of tandem beam and brazing clearance were varied. Sound butt joints could be obtained by using tandem beam with laser powers of 200-400W/100-150W even at the narrow gap brazing below 0.3mm where the melted filler metal did not infiltrate completely the joint gap by only using the main brazing beam (single beam). The tensile strength of the brazed joint using Ag-Pd filler metal increased with decreasing brazing clearance and attained about 70% of the base metal strength at brazing clearance of 0.1mm, while those using Au-Ni and Ag-Cu-Pd filler metals were comparable to the base metal strength at any brazing clearance between 0.1-1.5mm. The preheating during the tandem beam brazing resulted in superior brazability at the narrow gap to wide gap brazing because of the improvement in wetting/spreading and erosion esistance of melted filler metal by depressing the extremely high peak temperature and steep temperature distribution in the base metal.