The existence of Wat Mun San was first recorded in 1438. It was named after a government official with the rank of "mun" (10,000), whose work was concerned with royal documents, or "san"; hence, "mun san". It appears that in 1522 the monastery was a place where royal documents were being translated and many senior monks lived here. [In 1556, the town was occupied by the Burmese, who in turn were driven out by the Thais in 1775.]
The monastery was renovated in 1799, in the time of King Kawila of Chiang Mai, who brought the population of Ban Ngualai [also Pu and Kong] Community from the west bank of the Salween River to this location [as part of a program to repopulate the area after so many years of conflict]. These people were skilled silversmiths and formed the community "Ban Ngua Lai Mun San" with the monastery as its centre. There is a “Silver Temple” on the grounds that is completely covered by silver murals and decoration.
Wat Muen San was one of many facilities in Chiang Mai used by the Imperial Japanese Army (IJA) during the war. The wat was first occupied by Royal Thai Army troops; they were later replaced by IJA troops.
Following its failure to invade British India in mid-1944, the IJA are assumed to have established a field hospital on the grounds to treat incoming war casualties. Located on the southern outskirts of Chiang Mai, the hospital presumably received IJA troops arriving from the south and middle (central) supply routes emanating from Khun Yuam.
There is a memorial Museam on the grounds of this temple dedicated to the Japanese soldiers who fought in World War II. Its opening times seem to be somewhat of a mystery but you may be lucky enough to find it open.