Introduction: One of the important tasks for nurses is drug calculation that any mistake could lead to serious risks for patients.

Aim: This study was done for determining and comparing drug knowledge and drug calculation skills among critical and general nurses.

Method: In this cross-sectional study, 163 nurses were selected randomly from general and intensive care units in educational hospitals in Ahvaz in 2012. Intensive units were ICU ،CCU، Dialysis and Emergency Department. Data collected by a questionnaire consisting of two sections: demographic information and (40) questions in drug knowledge and (10) questions of drug calculations. Data was analyzed by descriptive statistic under software SPSS 16.

Results:  The results showed the (41.9%) general nurses and (39%) critical nurses were good, had not significant relationship. (75.3%) critical nurses and (65.1%) in general nurses were good in drug category, which had not significant relationship. (57.1%) critical nurses and (30.8%) general nurses were good and had significant relationship (P<0 /001), It means critical nurses was better than general nurses in that subject. Among expert nurses and non-expert nurses, knowledge of (39.2%) nurses who had less than (5) years’ experience and (46.2%) nurses who had more than 11 years’ experience, was good. While knowledge of (5.9%) nurses with less than (5) years’ experience and (15.4%) of nurses with more than (11) years’ experience was poor and the relationship between two group of nurses wasn’t significant (p<0.05).

Conclusion: In order to findings nurse managers might be rotate nurses between general and critical units for increasing their sensitivities' in drug calculation. Of course continuing education in drug calculation would be benefit, if they were applicable and specific for their units.