The aim of this research was to investigate the effect of co-authorship and self-citation on the citation rates of Iranian indexed articles in Web of Science (WoS). Research population included Iranian indexed articles in WoS in 2007 which had been received at least one citation. Numbers of articles in the time of research (October & November 2010) was 7355, which 390 of them, using stratified random sampling, was selected as sample. Research results showed that co-authored articles have received more citations than single-authored ones and this difference was statistically significant. On the other hand, self-citation exclusion has significantly reduced the citation rates of both co-authored and single-authored articles. After self-citation exclusion, existing difference between citation rates of co-authored and single-authored articles lost its significance. So, it can be concluded that self-citation exclusion led to reduction of citation rates of Iranian indexed articles in WoS, but this exclusion affected co-authored articles citation rates more than single-authored ones. In other words, high citation of Iranian co-authored articles in comparison with single-authored articles has been affected mainly by self-citation, not by foreign citation. This finding, which was our contribution, contradicted with results of previous researches.