Experiment, were conducted to determined the development of the vascular bundles in the peduncle of different tillers on its development in order to improve the vascular system and possibly increase grain yield. The development of the vascular bundle in the leaf, stem and panicle is an important aspect of assimilate translocation and differentiation of panacle characters. Two cultivars were used in this study : IR58, an indica type, and Unbong 7, a Japonica type. The main culm(M) had more and bigger vascular bundles in the peduncle and those vascular bundle decreased wish tiller order and tiller development. In the primary tillers, P1 had more large and small vascular bundles than P5 in both cultivars, IR58 developed more large vascular bundles compared to Unbong 7, but the small vascular bundle in unbong 7 was more than in IR58. The cross sectional area of phloem and xylem in large vascular bundle decreased with tiller order in both cultivar. Larger area of phloem and xylem in the early formed tillers more efficient transport of assimilates. The number of spikelets, the weight of panicle and grain yield per panicle were highest in the main culm followed by the order of their initiation or emergence. The number of primary and secondary branches to be positive associated with the number and area of vascular bundles. Furthermore, the number of vascular bundles in the peduncle was highly correlated with the peduncle thickness which in turn was correlated with the number of primary and secondary branches on the panicle. These results showed tillers that are initiated early and have relatively longer growth duration usually have more vascular bundles, larger peduncle, more spikelets per panicle, better spikelet filling and ultimately higher yield.