Hi All,
Is there any health insurance which can cover pre-existing diseases. I would like to insure my brother who is having hypertension. Please advise

Hypertension is not a disease, suresha. It is a condition meaning high blood pressure. I don't think you will find any restrictions for that unless there are other health issues with your brother that ascerbate the hypertension.

Tick

I can only speak for the US, most private insurance have waiting periods before they pay for pre existing conditions. A person in the US with Hypertension may have to wait for a year or two year for a policy to cover that.

If it is very bad, ( serious blood pressure issues) they may find it hard to get coverage