The aim of this study was to determine the LD30 values of the essential oils of Origanum minutiflorum He Schwarz-PH Davis (OM) and Juniperus excelca by Bieb.subsp. Excel (JE) in vivo investigation on the effects of malondialdehyde (MDA), vitamin C and some biochemical parameters. In this, study the essential oils of OM and JE plants were used. LD50 values of the essential oils were determined by using rats. OM (n=10), JE (n=10), carvacrol (n=10) which dissolve in olive oil were used as experimental group and as control group saline (SF) (n=8) and solvent Olive oil (n=10) were used and applied intraperitoneal on rats for 12 days in LD30 dosages. In the end of 12 days, Vit-C, malondialdehyde (MDA) and routine biochemical analyses were studied on their heart bloods. The difference in the levels of MDA and Vit-C was found significant among the groups (p<0.005). When the biochemical parameters of the groups were compared, all differences in all test were found significant (p<0.005) except for creatinine (p>0.005). When the values are put to paired comparison, the differences between groups were found statistically significant (p<0.005).OM and JE has led to significant changes in all lipid peroxidation and enzyme levels.