A SEX-STARVED shopkeeper was jailed for two years yesterday after admitting unlawful intercourse with a mentally retarded woman. Law Muk-chung, deprived of sex with his wife for a year, agreed he twice had sex with the 21-year-old woman, who has a mental age of nine. The District Court heard that on April 23 last year he stripped the woman and had sex in his shop and on May 9 he went to her flat where they had intercourse. Law, 38, changed his plea to guilty yesterday on two counts of unlawful sex with a defective. He denied two identical charges on which the prosecution offered no evidence. Katina Levy, defending, said Law had changed his plea to spare his victim the ordeal of reliving the incidents in the witness box. Last Friday Judge Wong adjourned the case, ruling the clearly distressed woman was unfit to testify against Law, who was denying all four charges. Mrs Levy said: ''Law had been deprived of sex with his wife since she became pregnant with their youngest son - for about one year.'' She said the victim visited the shop where Law was an assistant several times a day from late 1992. ''After he got to know the woman a bit he was under the impression, misguided or otherwise, that she fancied him,'' Mrs Levy said. On the first occasion they had sex, Mrs Levy said the woman stayed in the shop for a long time. ''He held the girl's hand and she held his. He felt affection and started having sex with her. After having sex with the victim he felt remorseful.'' But on May 9 the woman came into the shop and told him nobody was at home. So he followed her thinking she wanted to have sex with him, Mrs Levy said. She said Law had not realised the woman was mentally retarded as she worked in a factory and often took care of her two-year-old nephew. Judge Wong sentenced Law to a total term of two years. He said Law had committed a ''disgusting and rather serious'' offence. ''Having looked at the woman on Friday, one can immediately see that she is subnormal and needs to be protected,'' he said.