This is a list of notable events, premieres, releases, series cancellations, endings and other business ventures for Nickelodeon in the year 1998.
- April 4 - CatDog
- July 19 - Oh Yeah! Cartoons
- August 1 - You're On!
- August 31- Nickel-O-Zone
- September 1 - The Wild Thornberrys and Cousin Skeeter
- September 12 - Animorphs
- February 15 - I Didn't Do It season 2
- August 31 - Hey Arnold! season 3
- September 6 - The Mystery Files of Shelby Woo season 4
- December 12 - All That season 5
- October 16 - I Didn't Do It
- October 25 - The Mystery Files of Shelby Woo
- November 20 - The Rugrats Movie
- April 5 - The Rugrats from Nickelodeon comic strip debuts in around 70 papers nationwide.
- Bark, Spike, Bark!
- Jungle Trek
- The Rugrats and The Zombies
- Space Invaders!
- Tommy Catches a Cold
- Where the Sharks Are
- June 1 - Are We Having Fun Yet?: Activities Inspired by Nickelodeon Magazine
- September 1 - The Turkey Who Came to Dinner
- October 1
- November 1 - Family and Food and Orange Soda
- February 6 - Rugrats: A Live Adventure begins touring, starting in Wallingford, CT.
- January 13
- Hey Arnold!: Love Stinks
- Rocko's Modern Life: Modern Love
- February 3
- Rugrats: Diapered Duo
- Rugrats: Dr. Tommy Pickles
- February 24 - Good Burger
- April 7
- Gullah Gullah Island: Feelings
- Allegra's Window: Sing Along With Allegra And Lindi
- Little Bear: Parties And Picnics
- Rugrats: Mommy Mania
- June 30
- Blue's Clues: Arts & Crafts
- Blue's Clues: Story Time
- July 7
- Hey Arnold!: Partners
- Rugrats: Angelica Knows Best
- September 8
- Gullah Gullah Island: Christmas
- Little Bear: Good Night, Little Bear
Behind the scenes
- Nick Latino goes online.
- March - Nicktoon Studios opens in Burbank, California.
- June 1 - Citing competition and advertising problems, Nick shuts down its German service.Rugrats would later resurface on Pro Sieben (and SAT1 in January 2000), while most other Nicktoons find a home on RTL in Germany, and SF2 in Switzerland.
- June 6 - The cable industry held its second annual Tune In The Kids And Family week; on June 8th, 29 channels (including Nick), presented a multi-channel simulcast of Take A Moment, a variety special hosted by Melissa Joan Hart that stresses the reasons for the family to watch TV together.
- In the Summer, (Colossal) Pictures introduces a new theme of bumpers for Nickelodeon. Some include yarn-animated identification bumpers.
- August 10 - Nickelodeon becomes officially available in Brazil, though a Portuguese soundtrack was included on the Latin American version since it was launched in 1996.
- Fall - The Aquarius Theater in Hollywood (CA), was remodelled and renamed as "Nickelodeon on Sunset". This venue is the home of live-action Nick series taped in Hollywood, such as All That, The Amanda Show and Taina, as well as some concert specials produced for Nick.
- November 5 - Nickelodeon goes on the air in the Philippines.
- November 15 - Nickelodeon goes on the air in Japan, Malta, Russia (including the former Soviet republics) and Gabor Csupo's homeland, Hungary.
Nickelodeon character debuts
- Oh Yeah! Cartoons: Rudy Tabootie, Snap, Reggie Bullnerd, Horace T. Wilter, Timmy Turner, Vicky, Cosmo, Wanda, Mr. and Mrs. Turner
- Rugrats: Dil Pickles
- The Wild Thornberrys: Eliza Thornberry, Darwin Thornberry, Donnie Thornberry, Debbie Thornberry, Nigel Thornberry, Marianne Thornberry, Lady Thornberry