It happened just west of Fresno on California and Bryan.
Deputies said when they arrived at the home they found the girl who was accidentally shot by her 7-year old brother. She was shot in the torso and sustained a serious wound.
Fresno Sheriff's Office said she was sent to the hospital, where she underwent surgery and is listed in serious condition.
Fresno Sheriff's Office said they have brought in homicide detectives to examine the situation and to interview the brother.
They are not clear on who owned the pellet gun.
The Sheriff's Office says no arrests have been made.
Under California law, pellet guns are not required to be locked up, since they are not considered to be real firearms.