At the company's campus in the southern city of Shenzhen, workers turned up in costumes ranging from Spider-Man outfits to Victorian dresses.
The company had put on bands and acrobats in a stadium decorated with red banners saying "Care for and love each other".
The plant in Shenzhen, which includes bakeries, banks and acupuncture clinics, employs over 400,000 people.
Employees from other factories across China were shown live on giant screen for the event, which was titled "treasure your life, love your family, care for each other to build a wonderful future".
Foxconn said about 50,000 of its 900,000 workers in China were due to take part in the rally.
According to the following photos, being circulated in Chinese cyberspace, bolstering Foxconn CEO Terry Guo seems to have been a major focus of the rally organizers.
Foxconn workers hold a sign reading: "Grandpa Guo [Foxconn CEO Terry Guo], you work so hard!"
Sign reads, "Love me, love you, love Terry [Guo, Foxconn CEO]
"Heart Connects Heart"
"No worries, chief. A million hearts are following you."
"Our home is Foxconn; every day is bright."
"Life is Precious, Care about Family."
"Youth is like a song; sometimes you can't help but have discordant melodies."