The couple, who were living near the border with Mongolia, are being treated in Beijing and authorities have taken preventative measures.
Plague is caused by bacterium and comes in three forms – a lung infection, known as pneumonic plague; a blood infection, known as septicemic plague; and bubonic plague, which affects the lymph nodes.
The two affected have been quarantined for the pneumonic plague, which is the more serious form.
It comes six months after another couple from Inner Mongolia died of bubonic plague, which caused the Black Death in the Middle Ages, after eating the raw kidney of a marmot.
Plague is transmitted through infected animals and flea bites but pneumonic plague, which is highly contagious, can be spread when an infected person coughs.
Between 2010 and 2015, more than 3,248 cases were reported across the world leading to 84 deaths, according to the World Health Organisation.
Back in 2017 an unusually large plague outbreak killed 94 people in popular tourist island of Madagascar.
More than 70 per cent of the cases were of pneumonic plague, which can kill within 24 hours.