Abstract: A cap for a baby nursing bottle is provided with a stainless steel housed bimetallic thermometer probe. The probe is connected to a dial indicator with the mechanism hermetically sealed within a housing. The housing is either a separate metal and transparent window enclosure mounted in the crown of a plastic cap or an enclosure formed by a transparent window and a top wall of the cap. The complete assembly is suitable for use in microwave ovens. The bottle cap has one or more venting grooves for bypassing the thermometer housing or bottle mouth.