byte []b=.....
        System.Data.OleDb.OleDbConnection cn = new System.Data.OleDb.OleDbConnection();
        System.Data.OleDb.OleDbCommand cmd=new System.Data.OleDb.OleDbCommand("insert into tableName values (col1)", cn);
 
         cmd.Parameters.Add("col1",System.Data.OleDb.OleDbType.Binary,b.Length,"col1");
         cmd.Parameters[0].Value= b;
 
         cn.Open();
         cmd.ExecuteNonQuery();
         cn.Close();

...
cmd=new System.Data.OleDb.OleDbCommand("select * from tableName",cn);
         System.Data.OleDb.OleDbDataReader dr;
         dr=cmd.ExecuteReader();
         while(dr.Read())
         {
             byte []t=(byte [])dr[0];
             ....
         }
         dr.Close();

[Serializable]
public class Test
{
 
}
class MainA
{
   static void Main()
    {
        Test a = new Test();
        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        System.Runtime.Serialization.Formatters.Binary.BinaryFormatter bs = new System.Runtime.Serialization.Formatters.Binary.BinaryFormatter();
        bs.Serialize(ms, a);
 
        byte[] b = ms.ToArray();
        Console.WriteLine(b.Length);
    }
}