Abstract: To investigate the effect of source-sink manipulation on photosynthetic characteristics and yield components of wheat cultivars, a research was carried out in the greenhouse at the College of Agriculture, Shiraz University, Shiraz, Iran, during 2008-2009 growing season. Five wheat cultivars including Shiraz, Bahar, Pishtaz, Sistan (as bread wheat) and Yavaros (as durum wheat) were grown in 5 kg plastic pots. The source-sink manipulation treatments including defoliation of all leaves, defoliation of all leaves except the flag leaf, removal of 25% of spikelets and removal of 50% of spikelets were applied at anthesis. Results showed that number of grains per spike was significantly decreased by defoliation treatment in Shiraz, Bahar and Yavaros cultivars, so that in Shiraz and Bahar cultivars, source restriction reduced the number of grains per spike by 18.97 and 11.07%, respectively. In Shiraz cultivar, defoliation of all leaves decreased main stem grain yield by 40.75%, which demonstrated that Shiraz was very sensitive to source restriction. The little response of main shoot grain yield to defoliation in Pishtaz cultivar indicates high mobilization of photoassimilate from other parts of the crop to the grains. Under sink restriction conditions, wheat cultivars (except Pishtaz) had potential to increase their 100-grain weight; moreover, Pishtaz yield appeared to be more sink rather than source-limited. Removal of all leaves except the flag leaf at 8 and 18 DAA, in Pishtaz and Yavaros cultivars, had no significant effect on net photosynthesis rate (Pn) and in all cultivars except Pishtaz, sink restriction significantly decreased Pn rate. Further research, is recommended for improving our understanding on source-sink relationship in Iranian wheat cultivars.