The current study was carried out during 2010/2011 sugar beet season at the Experimental Farm of Sakha Agricultural Research Station for monitoring population fluctuations of Cassida vittata and isolation the entomopathogenic fungi, Stachybotrys sp. from this insect pest. Data indicated that the insect density gradually increased towards the end of the season to exhibit the highest density (175 individuals/20 plants) on 25 April-10 May. In a laboratory test, 17 adults of C. vittata out of 24 ones died because of the fungus, and the accumulated mortality, in a duration of 24 days, was calculated as 70.83%. This obviously show the virulence of Stachybotrys sp. in killing adults of C. vittata. In a field test, the suspension of Stachybotrys sp. (5 x 10⁴ spores/ml water) was sprayed on sugar beet plants against C. vittata. Mortality values of the insect one, two and three weeks post-treatment were 12.00, 12.50- and 11.76%, respectively. This investigation shows that this isolated fungus may be promising as an entomopathogenic against this beetle. However, further studies concerning biosafety and the effect of fungus applications in sugar beet fields on natural enemies are required.