In the production of biojet (SAF), which uses oils and fats as raw materials, In order to meet ASTM D7566 standards such as a pour point of -40 °C or lower, an isomerization and hydrocracking reaction is essential. Therefore, in order to obtain jet fraction with high yield, with the ultimate goal of SAF production, the authors first subjected n-hexadecane to isomerized hydrogenolysis and analyzed the resulting products in detail using GC/MS. And, the behavior of product selectivity in isomerization and hydrocracking reactions was investigated. The result, it was revealed that C₇-C₁₂ hydrocarbons containing a large amount of iso-paraffins, which corresponds to the jet fraction, were obtained at the high yield of 60 to 75 wt%. We also found that C₁₄ and C₁₅ hydrocarbons are produced in higher amounts than C1 and C₂ hydrocarbons and A non-stoichiometric decomposition phenomenon was occurring. In the reaction of n-heptane and n-pentane where the product is simplified, it has become clear that this non-stoichiometric decomposition phenomenon occurs. Although the authors were not able to explain this decomposition phenomenon, and, this decomposition phenomenon may allow jet fractions to be produced in high yields without producing products below naphtha fractions.