This experiment was conducted to investigate changes of the components in steamed and roasted green tea after 10 min, 20 min and 30 min of heat treatment of heat treatment at $110^{circ}C$. Vitamin C and tannin were determined by spetrophotometry. Total nitrogen, water-soluble nitrogen and water-soluble non protein nitrogen were determined by Kjeldahl analysis system. Aromas were identified by gas chromatography. After heat treatment, contents of most compounds decreased. Tannin and caffeine decreased a little bit, while vitamin C decreased considerably. There were both decreases and increases in aromas. Aromas which increased were geraniol, trans-2-hexenol, linalool, $alpha$-ionone and $eta$-ionone. From these results, it was concluded that the highest quality of green tea was one steam- treated for 10 min at $110^{circ}C$.