Lilo's Experiment Book is a log book/scrapbook seen in the Lilo & Stitch: The Series episodes "Drowsy" and "Snafu", as well as in Leroy & Stitch. The book has a small notepaper taped to the cover entitled Cousins. Lilo keeps a record of every rehabilitated experiment in this book with a photo showing each experiment, and the one true place they belong. At the end of Leroy & Stitch, a group photo of all the experiments in Lilo's extended ʻohana can be seen.
- Lilo keeps the book under her pillow on her bed.
- In Leroy & Stitch, Lilo took a picture of Stitch after deciding to let him be captain of the B.R.B. 9000.
- When a Leroy clone discovers the book and hunts down the experiments, he cuts the photo of said experiment he captures (including the one with Mertle and Gigi) by scratching an "X" onto it with his claw, thus destroying said photo. While he is doing this, the song "Hawaii Five-O" can be heard playing in the background.
- Stitch's photo is the only one that hasn't been scratched out, given that he, along with Jumba and Pleakley, were sent off to a black hole (which they managed to escape from).
- At the end, a group photo was taken with Lilo, Stitch, Nani, David, Jumba, Pleakley, and all the experiments.
- In the group photo, some of the experiments were not present.
- There were two errors in the group photo. Backhoe appeared twice: one visible on the rooftop, and the other visible on the stairs. Additionally, Phoon was shown twice: one in her normal form on the rooftop, and one in her mutated form on the porch.
- Mertle was in the photo since Gigi wanted to be in the shot.
- Reuben, 627, and Leroy are the only experiments that haven't had their photo taken in the book.
- Reuben was with Gantu the entire time, and after Gantu was reinstated as captain, Reuben was given a spot to be his galley officer.
- Since the experiments created before Stitch had been rehabilitated, it would be obvious for 627 and Leroy to not appear, as it was impossible for them to be rehabilitated.
- In "Snafu", Lilo was about to put the photo of Angel along with Stitch in the book; however, Stitch placed said photo in a hidden shrine under his bed.
- In regards to what happened to said photo when a Leroy clone obtained the book is unknown. It is possible that he either found Stitch's shrine, there was a spare photo of Angel in the book, a new photo was taken after Angel's rescue, or he didn't need one to know what she looked like once he found her.
- In its appearance in a Lilo & Stitch: The Series-themed Disney Tsum Tsum event held in September 2018 (in the Japanese version) and January 2019 (in the Global version), the book was used to represent the list of experiment Tsums to capture during the event.
- The Cousins title was written in a different handwriting style compared to how it appeared in Lilo & Stitch: The Series. In addition, the Japanese version of the event added the Japanese word for "cousins" (いとこ) underneath the English word.