Nick on CBS (also known as Nick Jr. on CBS) was a Saturday morning children's programming block on CBS that began on September 16, 2000, replacing CBS Kidshow. This Saturday morning block presented programming from Nick Jr. on Nick, which at the time shared common ownership with CBS under Viacom. When the block first properly aired, Face from Nick Jr. provided the continuity.
On September 14, 2002, the block was rebranded from Nick Jr. on CBS to simply Nick on CBS; at that time, its programming content expanded to animated Nickelodeon series aimed at children between 2 and 11 years of age, in addition to two Nick Jr. series.
As with the predecessor CBS Kidshow and Think CBS Kids blocks, all of the programs within the block complied with educational programming (E/I) requirements defined by the Children's Television Act, although the educational content in some of the programs was tenuous in nature. It was partly for this reason why some of Nickelodeon's most popular programs (most notably, SpongeBob SquarePants – at the time the cable channel's most popular series) were not included as part of the CBS block, even during the more open-formatted Nick on CBS era. However, some airings of SpongeBob SquarePants, The Fairly OddParents, Doug, Rocko's Modern Life, CatDog, The Adventures of Jimmy Neutron, Boy Genius, and Rocket Power appeared during special holiday events on the block. Rugrats also aired briefly in 2003, when it was added as a regular series within the block. Somewhere in early 2004, the network had a relaunch, making additions like live-action shows, such as The Brothers García.
In September 2004, the older-skewing Nickelodeon series were removed from the block, and Nick on CBS was rebranded back to Nick Jr. on CBS, refocusing the block back exclusively toward preschooler-oriented series; the block also began incorporating interstitial hosted segments featuring Piper O'Possum. On December 31, 2005, Viacom formally split under the shared control of National Amusements (owned by Sumner Redstone), with CBS and all related broadcasting, television production and distribution properties as well as some non-production entities becoming part of the standalone company CBS Corporation, while Nickelodeon and its parent subsidiary MTV Networks became part of a new company under the Viacom name.
Less than a month later on January 19, 2006, CBS announced that it would enter into a three-year programming partnership with DIC Entertainment to produce a new children's program block for the three-hour Saturday morning time slot featuring new and recent series from its program library, to begin airing in Fall 2006. On September 9, 2006, Nick Jr. on CBS ended its run, and was replaced with a new block the following weekend called KOL Secret Slumber Party.
Following the announcement of the second merger between Viacom and CBS Corporation, CBS CEO Joe Ianniello stated on an interview about the possibility of bringing Nickelodeon kids' programming to CBS on weekends, revealing a potential revival of the block.