In order to investigate the relationship between the expression of cyclin A and drug re-sistance in adult patients with acute leukemia (AL), the mRNA expression of cyclin A, mdrl, TopⅡα, bcl-2 was detected in 64 adult patients with AL and 20 normal controls by semi-reverse tran-scription polymerse chain reaction (semi-RT-PCR). It was found that the cyclin A and Top Ⅱα mR-NA expression levels in drug resistant group were significantly lower than in sensitive group (P ＜0. 01). Under the same experimental condition no cyclin A mRNA expression was detectable in allnormal controls. The mdr1 and bcl-2 mRNA expression levels in resistant group were significantlyhigher than in sensitive group (P＜0.01). cyclin A and Top Ⅱα gene expression levels were closelycorrelated (rs =+0. 794, P= 0. 000, n = 64) in all AL patients, but cyclin A was not correlatedwith mdr1 and bcl-2 gene expression levels. In drug resistant group there was a negative correlationbetween the gene expression levels of cyclin A and mdr1 (rs =-0. 337, P=0. 029). The 10 ALpatients with positive lower expression of both cyclin A and Top Ⅱα were all resistant to drugs. Lo-gistic regression of Binary analysis showed the correlation between the lower expression of cyclin Aand drug resistance. It was concluded that lower expression of cyclin A gene might be an unfavor-able prognostic factor for patients with AL, and detection of both cyclin A and Top Ⅱα gene expression would predict drug resistance in AL patients.