Jennifer Harrison, 38, swapped more than 100 X-rated texts with the prisoner at Doncaster's Lindholme jail, a medical disciplinary hearing was told.
The convict, referred to only as patient A, received 105 'sexts' from Harrison in just nine days, the General Pharmaceutical Council's misconduct panel heard.
Harrison, whose job at the prison was to administer medicine to inmates and carry out drug tests, was interviewed by South Yorkshire Police after the conversations came to light but no charges were brought.
The panel was told that the pair had begun a relationship in the summer of 2015 and in a nine day period in December of that year sent the convict 105 'rude' messages.
Panel chairman Christopher Gibson said: "She admitted that he gave her a phone number and that she kept it, and then used it to send him text messages, although she also admitted that she knew that prisoners were not allowed to have phones.
"She admitted that he had been telling her that he cared about her, and that she felt the same.
"She agreed that she had broken her position of trust after they started texting and she accepted that, after developing from general chit-chat, there were then a lot of feelings on both sides ending up with what she described as some rude things in the text messages.
"This was a situation where she was a pharmacy professional working in a prison with drug users of whom Patient A was one. It is essential, it seems to us, that such a relationship should be strictly professional and no more, and that it should remain strictly professional at all times.
"This relationship clearly transgressed that principle and, as Miss Harrison accepted, it clearly amounted to a breach of trust on her part.
"Even without direct sexual contact, we have no doubt that Miss Harrison was sexually motivated in her relationship with Patient A and in the sending of the text messages."
In her defence, she claimed she had been groomed by the inmate and had been involved in a controlling relationship with a different partner.
She has since stopped working as a pharmacist technician and was not represented at the hearing in London.
She was found guilty of engaging in a personal relationship with the inmate and sending him inappropriate messages.
The General Pharmaceutical Council misconduct panel ruled that her conduct was sexually motivated and ordered she be struck off.
‘Our order is that her name is to be removed from the register,’ added Mr Gibson.