The letter was dated 10 March, the day before the former Yugoslav president died in his cell at the detention unit of the UN war crimes tribunal in The Hague.
The letter, addressed to Russian Foreign Minister Sergei Lavrov, was delivered to the Russian Embassy in the Netherlands on 11 March, Foreign Ministry official Mihail Kaminin said.
Milosevic said in the letter that he was being subjected to inappropriate medical treatment and again asked for Russia's help in obtaining permission for treatment at a Moscow medical centre.
Milosevic's legal adviser Zdenko Tomanovic said on Sunday that the Serbian leader had sent a letter to Lavrov seeking assistance and insisting that he was being poisoned in the tribunal's detention centre with a leprosy drug.
"I consider constant efforts to deny me medical treatment in Russia to be motivated by fear that a careful expert analysis would expose ongoing active attempts to undermine my health, which could not be concealed from Russian specialists," Tomanovic quoted from the letter.
"Documents that were made available to me on 7 March show that on 12 January they found traces of an extremely strong medicine in my blood, which they say is used for the treatment of leprosy and tuberculosis, although I have not taken any antibiotics all these fives years while in their detention, nor have I had any infectious disease," the letter said.
"In any case, I cannot be treated by those who slip leprosy drugs (into my medication) or those against whom I defended my country and who have an interest in silencing me," Milosevic wrote.
According to Tomanovic, Milosevic said in the letter that he was really feeling unwell and that he needed medical assistance, and that he asked the Russian foreign minister to protect him from "criminal activities in the institution operating under UN insignia."