The Council Secretary General Thornbjorn Jagland said it was "the responsibility of Ukrainian authorities to ensure that Tymoshenko is treated appropriately and in accordance with Ukraine's commitments to the Council of Europe."
Tymoshenko is serving a seven-year term after being convicted in October of abuse of power.
Tymoshenko denies the charges and says her case is politically motivated persecution by her opponents.
A team of Western doctors reported last month she was "ill and in constant pain" and required blood and toxicology tests.
Her daughter has said she fears for her mother's life.
A delegation from the Council of Europe's committee on the prevention of torture visited Tymoshenko, along with the jailed former defense and interior ministers, Valery Ivashenko and Yury Lutsenko, in December.