The Shoushan National Nature Park is a unique uplifted coral reef mountainous terrain and a popular place for ecotourism, especially for the endemic and protected non-human primate species, the Formosan macaque (Macaca cyclopis). Human-monkey conflicts have been increasing over the last two decades due to growing habitat fragmentation, destruction of natural habitat, and population increase and range expansion of monkeys. We have monitored the changes of macaque population size and human-monkey conflicts. Scan, focal and behavior samplings were used as observational methods to record data on population dynamic, demography and social behaviors of macaques from 2012 to 2017. Besides, we analyzed patterns of macaque-tourist interactions recorded through ad libitum samplings. We followed 9 troops (464 individuals) with an average troop size of 51.5 (± 21.2) in 2012. Four group fissions occurred between 2013 and 2015 and the average size of 13 troops was 31.6 (± 17.3) in 2015. In 2017, only 10 troops with 330 individuals remained. At least 156 macaques disappeared, dead or injured and 28 of them had subcutaneous bleeding with confirmed rat poisoning. Mostly, macaque-tourist interactions did not occur. When they occurred, tourists initiated significantly more interactions than did macaques (89.4% versus 10.6%). The tourists initiated and acted mainly by gazing at them while passing by; they rarely revealed fear and showed hostilities with the exception of monkey grabbing food. By discouraging tourists from engaging in showing food or carrying transparent plastic bags, macaque threats could be reduced, thereby improving macaque-tourist interactions. The results shown in this study can enormously benefit the management of Shoushan National Nature Park by minimizing stress-induced human-monkey interactions.