Two new thermotolerant lactose consuming yeast strains, producers of thermostabile superoxide dismutase (SOD) (EC: 1.15.1.1.) were isolated and taxonomically identified as Kluyveromyces marxianus var. lactis T1 and Kluyveromyces marxianus var. bulgaricus T3. The influence of carbon source and growth temperature on the specific growth rate and SOD biosynthesis was also studied. Both strains grew well on lactose and/or lactose containing feedstocks and those substrates could be used for the production of SOD enzyme with high activity. Temperature of 40°C was proved to be suitable for cultivation of both strains with respect of SOD biosynthesis. Assay for thermostability of SOD enzyme of T1 and T3 strains cultivated on lactose shows that it is a thermostable one.