Abstract: In UV absorption，it is commonly to use molybdate -perchloric acid precipitant to deposit nucleic acid molecules in order to correct the interference caused by undistinguishable UV absorption with small molecules，it has been a routine experimental method for nucleic acid quantification and has been recorded many times in teaching materials. In this paper，the problems of molybdate - perchloric acid as precipitant has been discussed and an improvement method which used ethanol as precipitant was proposed. The detection method and conditions were determined through researching on the pH value of ethanol，the amount of ethanol，the precipitation time，the centrifugal speed and the centrifugal time. The results showed that the molybdate -perchloric acid precipitant had a strong absorption at 260 nm and this might result in detection error and poor reproducibility. However，with pH 3. 0 and 95% ethanol as a substitute precipitant，it had smaller error（below 5%）and better sample recovery（97. 7 ± 2. 1）%. The simplification，safety，easy operation and reliability features make this a good method for conventional quantification of DNA samples and also a good experiment example for teaching.

Key words: DNA quantification, UV absorption spectrophotometry, interference correction, improvement method, ethanol precipitation