Hi Sivansankar,

I don't know what plasmid you are isolating, which kit you are using, what cells, culture volume etc. but here are some recommendations for isolating plasmids

1. check if you have a high or a low copy plasmid. For low copy plasmids lower yields are normal and you might need to up-scale your culture

2. is your antibiotic working? If the antibiotic is to old/degraded you don't have selective pressure and the cells will loose the plasmid or you have overgrowth of cells with no plasmid at all. If you are not sure use a new batch of antibiotic

3. Avoid letting your culture get to dense/grow to long - some antibiotics get used up (eg ampicillin) during growth. When the concentration of the antibiotic gets to low you will loose selective pressure and cells with no plasmid will start to grow.

4. If the culture is getting to dense you might run into other problems like lysis and neutralization are not properly working - you might also overload your column and this will greatly reduce your plasmid yield. Check the OD of your culture (OD600: 2,0-2,4)

5. Use less of your culture to avoid overloading of the column

6. If you still have problems following these recommendations it sometimes also helps to use more antibiotic to have greater selective pressure

I hope this helps