Conversion citronellal to menthol has been investigated using catalyst Pt supported ZrO2-montmorillonite (Pt/Zr-MMT) with weight variation of catalyst. Menthol was important compound as feed and raw material for food additives, drugs, cosmetics and toiletries. Menthol can be isolated from Mentha arvensis or Mentha piperita plant, but due to huge consumption of menthol, isolation method only was not enough to supply the need so the conversion of menthol from citronellal oil were conducted. Chemically, menthol can be synthesized from several terpenoids such as citronellal. The conversion was conventionally conducted by two steps; cyclization and hydrogenation. The study was based on the principle of atom economy of a heterogeneous catalyst in the conversion of citronellal to menthol in one step. The research improved the method of conversion by considering microwave assisted organic reaction. Used that method, a fast, efficient and enviromental being process has been gained. Research focused on the synthesis of low cost, bifunctional and renewable catalyst based on Pt/Zr-modified natural clay. The reaction parameter of total conversion and total product were determined by gas chromatography analysis refer to citronellal and menthol standards. Results showed that bifunctional catalyst Pt/Zr-MMT gave significant contribution in menthol formation while Zr-MMT and raw MMT gave no menthol but only isopulegol as a product from cyclization mechanism. In concentration 0,4% Pt  with 0,01 gram weigth variation of catalyst gave lower conversion compared to 0,4% Pt with 0,03 gram weigth variation of catalyst. And concentration 1,0% Pt with 0,01 gram weigth variation of catalyst gave higher conversion than 1,0% Pt with 0,03 gram weigth variation of catalyst. At higher weight of catalyst, menthol can be produced. This was because the surface area of the catalyst Pt/Zr-MMT with 0,03 gram weigth variation of catalyst was greater than surface area of the catalyst Pt/Zr-MMT with 0,01 gram weigth variation of catalyst. 
Keywords: Menthol, Citronellal, Microwave, Platinum, ZrO2, Montmorillonite.