He used a knife to sever her head as they sat in his car
The couple had been seen talking animatedly several hours before her body was found in a village in Kazakhstan.
Teacher Shyngys Bekenov, 26, proposed to Nazerke Bekzhanova, 21, who had recently graduated from medical university.
But it is believed that she refused because her parents didn't approve of him.
“Furious” over her rejection, Bekenov used a knife to sever her head as they sat in his car, according to police.
The man then tried but failed to end his own life by stabbing himself in the abdomen after writing a suicide note asking that they should be buried together.
Bekenov has been detained in hospital in a “grave but stable” condition with knife wounds and will be moved to detention.
He faces a charge of murder with a minimum sentence of 15 years.
His note confirmed he had beheaded the woman after she told him she would marry him, it was reported.