Epilepsy is the expression of a functional paroxysmal neural impulses disturbance where neurons discharge excessive nerve impulses with a high frequency and abnormal synchrony. Investigations were conducted on a total of 45 dogs diagnosed with epilepsy aged between 3 months and 10 years. A number of 40 clinically healthy dogs were controll group (group M). Were determined plasma and erythrocyte magnesium, calcium, inorganic phosphate, potassium and sodium by molecular absorption spectrophotometry (colorimetric methods). In dogs with primary and secondary epilepsy has recorded a negative balance of magnesium with a statistically significant decrease of plasma and erythrocyte magnesium and also a negative correlation between attacks frequency-plasma and erythrocyte magnesium; the dogs with status epilepticus recorde the lowest levels of plasma and erythrocyte magnesium. The hypomagnesaemia, hypocalcemia and hyperphosphatemia recorded in dogs with secondary epilepsy are the important biochemical changes of magnesium deficiency syndrome with neuromusculare symptoms.