Ultramega OK is the debut studio album by American rock band Soundgarden, released on October 31, 1988, by SST Records. Following the release of the EPs Screaming Life (1987) and Fopp (1988), both for the Sub Pop record label, Soundgarden signed with SST and went to work on their debut full-length. The resulting album contained elements of psychedelic rock, hard rock, heavy metal and hardcore punk. The band supported the album with a tour in the United States, as well as its first overseas tour.

In 1990, the album earned a Grammy Award nomination for Best Metal Performance.

The album was recorded in spring 1988 in Seattle, Washington and Newberg, Oregon, with producer Drew Canulette. Frontman Chris Cornell said that during the recording sessions the band wasn't on the same page with Canulette. He said, "Material-wise we went through the process that we always do, but the producer wasn't used to the sound we wanted and didn't know what was happening in Seattle."

Later, in a 1995 interview, Cornell admitted "we made a huge mistake with Ultramega OK, because we left our home surroundings and people we'd been involved with and used this producer that really did affect our album in a kind of negative way. The producer was suggested by SST because they could get a good deal. I regret it, because in terms of material, it should have been one of the best records we ever did. It actually slowed down our momentum a little bit because it didn't really sound like us."

Around that same time, veteran Seattle producer Jack Endino, who also produced Soundgarden's first EP, Screaming Life, began the process of remixing the album, and actually completed a rough mix of "Flower". But, due to the band wanting to move on and the financial costs involved with re-pressing and redistributing the record, it was put on hold. The project resumed in 2014 by Jack Endino and Kim Thayil, and was completed in 2017.

Ultramega OK has elements of 1960s psychedelic rock, 1970s hard rock and heavy metal, and 1980s hardcore punk. Drummer Matt Cameron said that the band tried to refine its sound while still trying to keep an edge. Steve Huey of AllMusic said that the album is the "best expression of Soundgarden's early, Stooges/MC5-meets-Zeppelin/Sabbath sound", and added that it is "a dark, murky, buzzing record that simultaneously subverts and pays tribute to heavy metal".

Guitarist Kim Thayil recalls "Flower" as being the first time he blew across his guitar strings. This can be heard during the song's introduction, when they are played in rhythm with the drums. "Circle of Power" was one of the few Soundgarden songs to be written without any input from Cornell, as it was written by Thayil and bassist Hiro Yamamoto. It is also the only Soundgarden song on which Yamamoto performs lead vocals.

"Smokestack Lightning" is a Howlin' Wolf cover. On the original version of the album, "Smokestack Lightning" segued into a distorted excerpt from the Sonic Youth song, "Death Valley '69". Soundgarden included it as a tribute/parody of Sonic Youth's similar sampling of The Stooges song "Not Right" on their Bad Moon Rising album. This excerpt was removed from the 2017 reissue of Ultramega OK.