Ser-od's 2011 season started at the Northern 12-Stage Road Relay, where he led off the Morpeth Harriers team which went on to take the title. The 2011 London Marathon was his first major race of the year and he again had a top ten placing, taking ninth place in 2:11:35 hours to improve his best time a minute further. He finished in the top ten of both the 5000 m and 10,000 m at the 2011 Asian Athletics Championships, then went on to have his best global marathon finish at the 2011 World Championships in Athletics, finishing in 20th place. Two months later, he came sixth at the Beijing Marathon. In 2011 Hofu Yomiuri Marathon in Japan he defended his title as winner running for 2:11:56 hours improving his time by 2 minutes and 53 seconds than the previous year.