This study sought to investigate the influence of Facebook social-media usage on students' English written assignments in Eldoret North Sub-County public day secondary schools. The study adopted descriptive survey research design. The target population was 38 public day secondary schools with 15000 students and 88 Teachers of English in total. A sample of 150 students from a sample of 30% of the schools that was randomly selected was used in this study, which translated to 11 schools. Simple random sampling technique was used to selects the schools. Purposive sampling technique was used to select all teachers of English who participated in the interview and simple random sampling technique was used to select the students who filled questionnaires. Questionnaires, interviews and document analysis was used in data collection. Majority of the respondents agreed that they pay little attention to spellings when posting opinion on facebook, because friends care less about spelling mistakes. Most respondents agreed to get the meaning of shortened form of words used by their friends on Facebook. Most respondents agreed that they regularly use short forms of words when posting information on Facebook Social-media. The study established that sometimes students find themselves using the short forms of words when writing English assignments. Majority of the respondents agreed with the opinion that most of the opinions written on Facebook are presented in short forms. The students use short forms when commenting on their friends post on