Citation rate is commonly regarded as a measure for determining the performance of individuals working in academia. Previous studies using archival data found that the alphabetical order of researchers' surnames influences their citation rate. However, the causality in their findings was limited because their methodology could not rule out alternative explanations, and the effect of the order on in-text citation decisions across different citation systems has been under-investigated. Accordingly, the present study experimentally manipulated citation systems and the alphabetical order of first authors' surnames in a hypothetical article. Our findings indicate that references from first authors with earlier (vs. later) alphabetical order surnames were more likely to be cited. This effect was stronger under the alphabetical citation system compared to the numerical system. Practically, these findings highlight the need for improving the alphabetical citation system to enhance the communication and dissemination of knowledge and objectivity in evaluating scholars' research impact.