The paper represents the results of metallographic investigation and x-ray spectral microanalysis of permanent joints of dissimilar molybdenum–stainless steel materials, which are made using radiation heating in a vacuum and brazing filler metal of copper–manganese–nickel system. Influence of brazing temperature mode on joint formation and formation of brazed seams’ structure is studied. As shown, the brazing of molybdenum–stainless steel flat lap joints at temperature of 1100°C provides formation of smooth fillets and impervious brazed seams, and dispergation of base metal (stainless steel). Local x-ray spectral microanalysis determines that copper-based solid solution and dispersed particles of stainless steel (of about 20 $\mu$m in size) are the structural constituents of brazed seam. Interaction between liquid brazing filler metal and solid material being brazed takes place at the brazing temperature that results in enriching of the seam by the elements of brazed dissimilar metals. Diffusion processes at molybdenum-brazing filler metal interface promote formation of a molybdenum-based diffusion layer containing (wt.%) 22.27% of iron, 7.29% of chromium, 4.11% of nickel, 0.84% of silicon, and 0.71% of copper. It precipitates in a form of continuous band of about 2 $\mu$m thickness along the brazed seam at molybdenum side. Copper-based solid solution also contains stainless steel elements such as iron and chromium, but in significantly lower quantity 3.27–3.45% and 0.62–0.64%, respectively. Reduction of the brazing temperature to 1084°C allows eliminating base metal dispergation and provides formation of single-type brazed welds’ seams. A matrix of brazed seam is presented by copper-based solid solution containing such concentration of elements as in seam brazed at higher temperature. Insignificant area of a vision field (of about 1%) is covered by precipitations of the particles enriched in 5.78% of molybdenum and constituent elements of stainless steel, i.e., 39.54% of iron and up to 8.58% of chromium. Width of diffusion layer reduces to 0.9–1.4 $\mu$m, but relationship of concentrations of chemical elements is kept the same. Penetration of brazing filler metal (solid solution) over the grain boundaries of brazed metal (stainless steel) is observed in some areas of the weld.