The superstar, 62, had told reporters over the weekend that he wanted to adopt 14-month-old boy Lev after meeting him during a visit to an orphanage.
Speaking to The AP, the country's minister for family affairs Yuriy Pavlenko said: "Foreign citizens who are single have no right to adopt children... and the age difference between the adopter and the child cannot be more than 45 years.
"The law is the same for everybody - for a president, for a minister, for Elton John."
Pavlenko went on to say that the singer's civil partnership with David Furnish would not be recognised as marriage in Ukraine.
However, he insisted that the country is grateful for John's charity work and hoped that his adoption plea will prompt more domestic adoptions of children with health problems.
> Elton adoption comments worry charities