Although we have put much attention and effort into the treatment and prevention of sexual offending in the past few years, sexual assault to female victims with mental retardation (MR) cases are still rampant in Taiwan. To further explore the situation of sexual victimization for the female MR victims, the present study sampled purposefully 12 sexual offenders from 3 prisons, e.g. Taipei Prison, Taichung Prison, & Kaohsiung Prison, and interviewed the subjects on the topics about the motivation of offending, the situation and condition of the case, their knowledge about the victims and their strategies for seduce, their thought about how to choose the target, the process of offending, their thinking and response about the offending. Nine out of the 12 interviewees admitted that they had known the MR victims or had been very familiar with them. Most of the offenders thought that MR female were easier to be seduced, so that they were active in creating the situation for get-together or seducing with food or money once they found adequate chance. Over half of the interviewees said they had learned the victim's intellectual condition, so they took action to attack the victims and encountered no reluctance. High rate of the offense took place in the noon or afternoon when many protectors thought the time period being safe. The families or guardians of the victims with mild MR made wrong judgment so as to let the girls more freedom to stay alone in parks or neighborhood, since they considered the girls were able to communicate and protect themselves. Based on the research findings, the authors propose the following points: 1. Acquaintance rape often occurs between girls with MR and their families, relatives, neighbors, or other known persons, because that the MR victims had been weak in self-protection under no adequate guardian. 2. Adequate education or training should be provided for the mild MR female for them to abiding by the principle of sex autonomy and self-protection when interacting with persons. 3. Strengthened care, observation and guard should be provided for the moderate and severe MR female. 4. There should be no time gap (day time or afternoon) in protecting MR female. 5. Educating the general public for them to understand the characteristics of the MR female and to break rape myths are critical points for preventing sexual assault.