Abstract: The main chemical composition was analyzed in the normal and poorly cured tobacco leaves in the cutters and upper leaves (cv. K326) in order to understand the quality difference between poorly cured tobacco leaves and the normal. The results showed that the contents of total sugar, reducing sugar and the ratio between sugar and nicotine were significantly reduced in the poorly cured tobacco leaves in contrast to the normal. But the contents of nicotine, total nitrogen and protein were higher in the poorly cured tobacco leaves than those in the normal. So the main chemical composition in the poorly cured tobacco leaves was in inappropriate or grossly inappropriate. The average of total sugar and reducing sugar contents in poorly cured cutters was 53.5% and 50.6% lower than those of normally cured C3F leaves. At the same time, the average in poorly cured upper leaves was 39.6% and 35.3% lower than those in normally cured B2F leaves. The average of nicotine, total nitrogen and protein contents in poorly cured cutters was 31.4%, 40.6% and 28.6% higher than those in normally cured C3F leaves. Simultaneously, the average of poorly cured upper leaves was 24.5%, 36.4% and 21.2% higher than those in normally cured B2F leaves. The average of reducing sugar/nicotine in poorly cured cutters was 62.0% lower than those in C3F. The average of poorly cured upper leaves was 47.8% lower than those in B2F. It follows that the main chemical composition in poorly-cured tobacco leaves is inappropriate for cigarette production.