Personally I would say August/September/October. The weather is the nicest then and it is a much less touristy time of year to travel to Mongolia. You will miss Naadam festival, however there are still plenty of festivities in Mongolia during this time. Ulaanbaatar gets a bit crazy during June and July with tourists and pickpockets out in full force. It doesn't suit Mongolia, as the vibe is generally relaxed and the people are easy-going. Especially in the country side!

During Naadam in July 11-12st. best period.Naadam is nice in villages out of the UB.More close to Nomad's life and nature.

I agree- July for Naadam is great. Try to get to one of the smaller towns for their Naadam (the exact dates are all different, but I'm sure you can find out online). Less crowds, better entertainment. Although I am partial to the Gobi in the winter- if you go then, be sure to pack plenty of very warm clothes if you're leaving the city. There's not much for roads outside of UB, and if your bus/meekr/jeep breaks down (or its heater doesn't work), you'll freeze.

July and August. Best temperatures and spectacular grasslands!

In the middle of July - for the Nadaam festival.

I was there in August and it was extremly hot in eastern Mongolia and rather cold in western part - near Hovd. When i was in mountains near Hovd I was suprised by hard snowfall. It is better to travel in summer, becouse in winter roads (and off-roads), are hard to handle...

You should definitely go for the Naadam Festival in July. It is a fascinating experience! Weather is good and you'll get to see the many colors and cultures of Mongolia. Maybe even try your own hand at ankle-bone archery! Went with Intrepid Travel. Pics are on duwakahuna.com.

I was there in august, and there around 20th of August comes the winter. 1 day it's extremly hot, but next day in the middle of the night it's zero degrees. So a little bit earlier it could be nice.

I was there in Mid May last year and the weather was pleasantly warm. Didn't need much of a jacket most of the time (except at night). There were so few tourists at that time, that it was nice. If you don't mind lots of tourists, go in summer when it is even warmer. If you want to go to the Nadaam Festival, then definitely go in July.

The best time is summer. In July the Nadam festival is great.

June-August are defintiely the popular times to visit, especialyl durignthe Naadam festival. You may want to consider the September-October timeframe if you're not only interested in the "best" weather. While Naadam has becoem very popular with tourists, the Golden Eagle Festival in western Mongolia happens around early October and is a great Kazakh culture event.

June, July, August and September are the best months since they are in Mongolia's brief summer season, when temperatures are pleasant. However June and September can still be a bit chilly. July is the month of the Naadam Festival, an event not to be missed. August can see a bit of rain, but it rarely lasts all day. Mongolia's winter is harsh with sub zero temperatures throughout the country. Spring is not usually recommended, as people and animals can seem a bit disheartened after the long winter months. Mongolia's weather is very changeable and you will need to carry warm clothes with you even in summer, since it is windy most of the time and there is not much you can do not to be exposed to the elements. Apart from your tent/ger or vehicle, you are not likely to get much shelter from the wind, rain or sun. It can bit very hot one minute and bitterly cold the next. This is particularly the case in Western Mongolia where the weather is more extreme due to higher altitude. Mongolia is known as the Land of Blue Sky, so you should get plenty of sunshine year round.