Sandra Tennyson is Carl Tennyson's wife and Ben's mother. She is first introduced in the first live-action movie, Ben 10: Race Against Time. She wants Ben to call her "Sandra" not "mother", "mommy" or "mom".
Sandra made a cameo in the first episode, when she was washing dishes and yelling at Ben for running in the house. However, she was a brunette at the time.
In Grounded, Sandra and Carl witnessed Ben and Gwen fighting a Highbreed. She and Carl became angry at Ben for lying to them so many times and forbid Ben from using the Omnitrix. However Ben disobeys them when Kevin is in trouble. Sandra and Carl spot Echo Echo trying to sneak out of the house and then he is grounded. Ben later blatantly disobeys them and transforms right in front of them to leaves and help Kevin, and Sandra and Carl realize Ben is trying to protect the Earth, and they realize they were wrong to stop him, they then decide to go help Ben save Kevin. Carl and Sandra save Humungousaur and Kevin from the Highbreed using a Space-Bazooka.
Sandra returned in Hit 'Em Where They Live, where she along with Ben's family are attacked by Ben's enemies. When she was washing dishes, she was ambushed by Sevenseven without realising, but was saved by Max. Later in the episode, she was kidnapped by Zombozo and taken to an abandoned carnival. She was saved by Gwen.
- In "Ben 10 Returns: Part 1", Sandra was a brunette, instead of a blonde, like she was before and after that episode, making it unclear which one is her natural hair color.
- Sandra seems to contradict Carl when it comes to disciplining Ben, being more stern, though like Carl, she insisted to be called Sandra.
- Sandra's name is pronounced differently in the movie than the series.
- Sandra does not appear to be fond of Kevin much; calling him Ben's "ruffian friend". Despite this, she approves of their friendship.
- In Ultimate Alien, Sandra seems to have a liking for health and fitness, as shown in "Hit 'Em Where They Live", where she she was seen exercising in a fitness ball and also rejected Gwen's offer of cotton candy, stating that processed sugar is poison.