BANGKOK, 19 Jun 2015 (AFP) - Six birdies including four on the back nine put him on an eight under par 134 after two days play on the Thai island.
His round, which included a 30-foot birdie putt on the tenth hole, means Thai players have led after both days' play so far.
Prayad said a victory for his compatriots was a must in an event named after his nation's Queen Sirikit.
"Before the round, I told myself it does not matter who is leading, as long as it's a Thai leading, I am ok with it," he said according to an Asian Tour statement.
"I didn't expect myself to lead now but I am happy with where I am right now. I hope I can help keep the trophy on home soil this week."
Canada's Richard T. Lee led the chasing pack at six under for the Asian Tour tournament and could have been closer were it not for a bogey on the 11th.
Surprise round one leader Attaphon Sriboonkaew showed his impressive first round 66 was no fluke, going round in 71 to keep him in contention at five under for the event.
That left him level with compatriot Thaworn Wiratchant going into the weekend.
Leading scores after round two:
134 - Prayad Marksaeng (THA) 69-65
136 - Richard T. Lee (CAN) 69-67
137 - Atthaphon Sriboonkaew (THA) 66-71, Thaworn Wiratchant (THA) 69-68
138 - Wolmer Murillo (VEN) 72-66, Danny Chia (MAS) 69-69
139 - Siddikur Rahman (BAN) 69-70, Thanykon Khrongpha(THA) 74-65, Wang Jeung-Hun (KOR) 68-71, Chinnarat Phadungsil (THA) 68-71