Background: During the period of January to February 2017 there were no reports regarding the incidence of sharp injuries at RST Dr. Soedjono Magelang. The report is different from the findings obtained by the researchers through interviews with three nurses in the internal medicine ward having experienced a needle stick injury when they mix the drug to be given to the patient. Understanding of sharp safety is an important thing in preventing and handling the incidence of sharp injury. However, the time factor is often a consideration because health workers often work in shifts so that they cannot afford to take part in the overall activity. Therefore, the authors conducted a study to determine the role of Online Learning in improving understanding of sharp safety in health workers in the RST of Dr. Soedjono Magelang. Methods: This research is a quasi experimental study. The design was carried out by giving a test at the beginning and end of a single group study sample. Population & sample was taken from RSM by purposive sampling. Data capture was taken between May-July 2018. Online-learning instrument use: Sharp Safety module Smartphone, Whatsapp group and web as repository, and online Questionaire. Results: There were 19 respondents of health workers consisting of 7 doctors, 11 nurses and 1 administrative officer who were willing to take sharp safety module classes in the Whatsapp group. The use of online learning about sharp safety for health workers in RSM is considered quite effective from the significant increase (p = 0,000) between the pre-test and post-test scores. There was an increase in results in 17 respondents, while 2 respondents got the same results between pre and post test. Conclusion: Online learning improves understanding of health workers at RST Dr. Soedjono, Magelang regarding sharp safety significantly to safety devices, safety procedure, vaccination in sharp safety, reporting after sharp injury, monitoring and evaluation of post sharp injury, and regulations regarding sharp safety. Whereas knowledge about the implications of sharp injury and infections related to sharp injury did not increase significantly. Keywords: Online learning, sharp safety, sharp injury