Jitendra,
There is no provision in any act to make medical insurance compulsory for individuals working in any organisation.
However, as members have pointed out, under Workman Compensation Act (now called Employee Compensation Act), in case of injury in the course of employment, the employer will be liable to pay the cost of treatment for those who are not covered under ESIC. To protect the company, it is recommended that the company take WC Policy to cover the risk stated above.
For those with salary of less than 21,000 a month, ESIC is compulsory in the areas which are notified (and in organisations with more than 10 employees). that is a form of medical insurance.
Other than ESIC, there is no mandate in law for compulsory medical insurance.