Quantitative investigation is made on the elemental segregation in different zones of a heavy microalloyed cast steel by energy dispersive X-ray spectroscopy. It is demonstrated that C shows serious segregation tendency than that of Mn and Si, and the degree of C segregation in the surface zone is higher than that in the central zone. C enrichment is generally observed at both dendrite arm and grain boundaries, and more C segregation at dendrite arm boundary in contrast to that at grain boundary is found in this steel. The distribution of C concentration shows a decreased trend from root to tip along the dendrite arm boundary. The C concentration at trigeminal boundary intersection shows higher level than that at other position of the grain boundaries.