Ultar Sar (also Ultar, Ultar II, Bojohagur Duanasir II) is the southeasternmost major peak of the Batura Muztagh, a subrange of the Karakoram range. It lies about 10 km (6.2 mi) northeast of the Karimabad, a town on the Karakoram Highway in the Hunza Valley, part of the Gilgit District of the Northern Areas of Pakistan.

While not one of the highest peaks of the Karakoram, Ultar Sar is notable for its dramatic rise above local terrain. Its south flank rises over 5,300 metres (17,388 feet) above the Hunza River near Karimabad, in only about 10 km (6.2 mi) of horizontal distance. Combined with its strategic position at the end of the Batura Muztagh, with the Hunza River bending around it, this makes Ultar a visually striking peak.

Ultar Sar also gained fame in the 1990s as supposedly the world's highest unclimbed independent peak. This was incorrect, as Gangkhar Puensum in Bhutan is higher, and remains unclimbed (and off-limits) in 2007. (Two other higher peaks are also reputedly unclimbed and of independent stature.) However that perception did add to the appeal of the peak, and a number of expeditions attempted to climb it. During the 1980s and 1990s over 15 expeditions made attempts, resulting in no success, but in a number of fatalities; the peak proved to be quite difficult.

The first two ascents were made in July 1996 by two separate Japanese expeditions, the first (from the Tokai section of the Japanese Alpine Club) led by Akito Yamazaki (who summitted, but died on the descent) and the second led by Ken Takahashi. The first summit team comprised Yamazaki and Kiyoshi Matsuoka (who died one year later on the nearby peak Bublimotin). They climbed the peak from the southwest in alpine style, doing much of the climbing at night to avoid danger from falling rock and ice. After their successful summit, they faced strong storms and bivouaced several days without food before returning to basecamp. However, Akihito Yamazaki died at basecamp of an internal disease due to the severe stress of climbing.