Background Central venous catheter (CVC) is of extreme importance especially in critical care units. To perform confident CVCs, nursing students should acquire an appropriate theoretical and practical knowledge during their course of study. ELearning is one of the new methods of teaching in medical sciences. The aim of this study was to determine the effect of eLearning on the cognitive learning of senior nursing students concerning central venous catheter. Methods This is a quasi-experimental study with a one-group, pre-post-test design. The study was conducted in the 2015 - 2016 academic year. A total of 40 students (12 males and 28 females) in the 8th semester were selected through simple randomization sampling method from May to July 2016. Their knowledge about CVC was assessed before and after the intervention using a questionnaire that consisted of 20 areas. After the pre-test was administered, the learning content was presented to the students through the eLearning portal. The collected data were analyzed in SPSS software using paired t-test, independent t-test. The significance level was set at P < 0.05. Results Paired t-test showed a significant difference (P = 0.001) between the average scores of knowledge before and after intervention. There was no significant association between knowledge scores and age, gender, place of residence, grade point average, clinical experience, experience with CVC, and satisfaction with eLearning. Conclusions It seems that eLearning can increase students’ knowledge about CVC. Thus, this method is recommended for teaching nursing courses.