Wash the bottle with warm water and soap using a bottle brush. Rinse the soap off the bottle.
Place the bottle, its cap and its nipple inside of a microwave sterilizer bag. Pour 120 ml or about 4 oz of clean drinking water into the bag and seal it tightly.
Place the bag on the turntable of a microwave. If the microwave doesn't have a turntable, place the bag on the floor of the microwave. Do not put it on a metal rack if the microwave is so equipped.
Heat the microwave for two minutes at 1100 watts, three minutes at 800 to 1100 watts or five minutes at 500 to 750 watts. The time depends on the wattage of the microwave. You can usually find this on a label either on the front, sides, bottom or rear of the microwave.
Remove the sterilizer bag from the microwave after it has finished using oven mitts. Hold the bag away from you at arm's length over a sink and let the hot water pour out through the steam vent. Keep this vent away from your face.
Open the bag and remove the bottle, cap and nipple. Dry the parts with a paper towel and store them in a zip-lock bag or plastic container with a lid.
