Pierre Jartoux’s Brevis vitae ratio is an autobiographical memoir in Latin, sent by the French Jesuit to the Society’s General in Rome. The memoir contains fresh information on the author’s personal story, on the troubled history of Beijing’s mission in the last period of Kangxi’s reign, and on the emperor’s scientific studies with the Jesuits as well. Notably, the last part of Jartoux’s text is devoted to his meeting with the highest authority of Mongolian Buddhism at the time, the Jebtsundamba Qutughtu Zanabazar, and the brief religious ‘dispute’ between the two. The text was written very likely in order to protest against the Visitor Giovanni Paolo Gozani’s policy towards the French Mission and, more generally, against the Portuguese attitude towards them. This annotated edition includes a full transcription and translation of this little known memoir.