Abstract: For determination of total molybdenum in its ores, the sample was heated with HCl and fumed with mixed acid of HNO3 and H2SO4(8+2) to dryness. Instead of the alkali fusion, the residue was treated with 150 g·L-1 NaOH solution to transform molybdenum into molybdate, and content of total molybdenum was determined in the supernatant. For dissolution of different phases of molybdenum ore, a separate sample was first heated with aqueous ammonia to dissolve the molybdite (MoO3), and insoluble residues obtained from each step of dissolution were treated with 40 g·L-1 tartaric acid solution and 150 g·L-1 Na2CO3 solution in succession to separate the phases of calcitungstomolyoxide ［Ca(W,Mo)O4］ and lead molybdate (PbMoO4) respectively. The molybdenite (MoS2) was in the residue remained after dissolution of PbMoO4, and it was ignited at 580 ℃ and then treated in the same way as for determination of total molybdenum with HCl-HNO3-H2SO4 and NaOH solution, as described above. Finally, contents of molybdenum in each of the above mentioned solutions were determined by catalytic polarography in a base solution containing KClO3, diphenylglycollic acid, diphenyl guanidine and H2SO4. In the analysis of 3 standard samples of molybdenum ores, contents of sum of the 4 ore phases were found to check quite well with the contents of total molybdenum found, with values of RSD′s (n=5) less than 3.5%.