The purpose of this study was to examine the effect of CoQ₁₀ supplement consumption during tapering phase on some of endurance performance indices in middle distance runners. To do this, 18 trained middle distance male runners with an age of 21±1.26 years old, a weight of 65.6±4.7kg and height of 179±2.5 were selected.  This study was based on the pre test - post test method with two experimental groups and one control group. Study subjects were prepared for the pre test after 10 weeks training to increase aerobic and anaerobic endurance, lactate threshold, lactate tolerance under 70-95% MHR and 4 sessions training in one week (70-90 min/session). The pre test was then conducted which included  rest heart rate (RHR), sub maximal heart rate (SubHR), maximal heart rate(MHR), 1mile test and time to exhaustion (Tex) (pre-taper). After that, the pre test participants were divided into three equal groups including T+Q10 (i.e. 1week tapering with Q10,120 mg/day), T (i.e. 1week tapering with placebo) and C (i.e. continued previous training with placebo). In the tapering period, the volume of training progressively decreased and  its intensity increased to 135% of Vo2max while the frequency was constant. At the end of the tapering period (POST taper) all previous tests were measured respectively. To investigate mean differences between PRE and POST-test variables, the dependent student t-test was selected, and for the analysis of mean differences between the groups ANOVA was used. The obtained results showed that there is a significant decrease in RHR and SubHR in the groups of  T and T+Q10. The 1mile test record and Tex were significantly improved (P<0.05), whereas there was no difference in MHR (p>0.05). It may be concluded that the COQ10 consumption in the tapering period has no significant effect on variables considered (p>0.05). Similarly, no significant change was experienced in the variables after one week in group C (p>0.05). In conclusion, the obtained results demonstrated that the COQ10 supplementation with one week tapering period has no effect on the performance of variables considered in this study. However,  the tapering period could improve the RHR, SubHR, Tex and 1mile test performance with no effect on MHR.