1 Place the tenderloin in a roasting pan. 2  Place the pan in the oven and roast for about 15 minutes, or until the internal temperature reaches 145 degrees Fahrenheit (63 degrees Celsius). 3  Allow the pork to rest for 10 minutes before serving. Place pork tenderloin in roasting pan. 2  Roast for 30 minutes. 3  Turn the pork over and roast for another 25 minutes. 4  The pork tenderloin is ready when the internal temperature reaches 145 degrees Fahrenheit (63 degrees Celsius).