In 1998, he was arrested and sentenced to 7 years imprisonment, charged on the basis of an intercepted  letter from an erstwhile 'comrade' which listed names of those to be contacted to see if they were still interested in opposition activity. He was unaware of the letter until his arrest. After sentence, he was transferred to Mandalay Jail, where he was forced to improvise to continue painting. Using the white cotton prison uniform as a canvas, he paid for paints to be smuggled into the jail. In the absence of brushes, he used his fingers, cigarette lighters, syringes, carved soap, and dinner plates to make his mark.   In Mandalay he performed a piece ‘0 + 0 + 0 = 0’  (1999) for the amusement of his fellow prisoners.

Conditions in Mandalay jail were particularly harsh, and in 2000 political prisoners in protested for better conditions, including in Htein Lin’s case, the right to paint.    The protesters were beaten and dispersed to other jails and he was sent to Myaungmya in the Irrawaddy Delta, a small town where George Orwell spent three miserable months on his first posting as a colonial police officer.  Htein Lin was punished with seven months spent in solitary confinement on death row in the jail, built by the British in 1900. Happily conditions in Myaungmya were not as bad as Mandalay for most of the time, and it was not far from his hometown. Once out of solitary he continued to paint, using the same techniques and materials he had developed in Mandalay