Evidenced based practice (EBP) guidelines have been developed to reduce variation in weaning, provide quality of care and patient satisfaction. Nurse led weaning has been shown to reduce weaning time, and therefore it was important to identify whether nurses have sufficient knowledge to implement EBP regarding weaning (Hansen, Fjaelberg, Nilsen et al, 2008);(Crocker, 2002:272). Weaning protocols are associated with 25.0% reduction in the duration of mechanical ventilation time, a 78.0% reduction in weaning duration, and 10.0% reduction for length of stay in ICU (Blackwood, Alderdice, Burns et al, 2011:9). The purpose of the study was to evaluate and describe intensive care nurses’ knowledge of EBP guidelines with regard to weaning the mechanically ventilated patient. Five adult intensive care units at two tertiary public sector academic hospitals were used to conduct the study in order to determine barriers to EBP. A non-experimental, descriptive, prospective two-staged design was utilized in this two part study. In Stage I of the study, the sample size comprised six (n=6) specialist expert members selected from the ICU’s at the study site using a non-probability purposive sampling method. In Stage II of the study, the sample size comprised eighty (n=80) intensive care nurse respondents selected from the ICU’s using simple random sampling. The data collection instrument developed by the researcher comprised 40 items relevant to nursing practice derived from EBP weaning guidelines. Respondents were asked to rate all the items independently using a 4-point Likert scale. Findings indicated that intensive care nurses lack adequate knowledge on weaning the critically ill patient from the mechanical ventilator. The Dreyfuss model of skill acquisition shows that improved skill performance in nursing is based on experience as well as education, yet this study showed the opposite (Dracup & Bryan-Brown, 2004). Years of experience did not influence nurses’ knowledge level, as there was no statistical difference in these items. Differences in knowledge scores between the primary nurse and shift leaders were minimal, although significant (p<0.05), indicating that shift leaders were more knowledgeable than primary nurses.