how to get Client MAC address by using server side language

You can get client's IP address using following code,

Request.UserHostAddress

The MAC address isn't in the client request headers, so the only thing you've got in the clients IP address to use. You can't get the MAC address of the client unless the server is on the same network segment as the client.

What'll happen is you'll get the clients IP address, try to resolve it to a MAC using ARP, but then you'll find that the MAC you get back is the same for just about all of your clients (depending on network layout) and it's the MAC for the routers near-side interface. This is the first hop from the server back to the client.

use this c# code

MACAddress = MACAddress.Replace(":", "");
Response.Write(MACAddress);

string macAddresses = "";
foreach (System.Net.NetworkInformation.NetworkInterface nic in System.Net.NetworkInformation.NetworkInterface.GetAllNetworkInterfaces())
{
    if (nic.OperationalStatus == System.Net.NetworkInformation.OperationalStatus.Up)
    {
        macAddresses += nic.GetPhysicalAddress().ToString();
        break;
    }
}
Response.Write(macAddresses);