Elizabeth March, called Beth, is the third March daughter. At thirteen when the story opens, her family faces poverty after her father's financial loss. Profoundly shy and socially anxious, Beth finds leaving home deeply uncomfortable and is homeschooled.

Gentle, kind, and selfless, she avoids conflict and acts as a peacemaker among her sisters. Her interests center on playing the piano, caring for her dolls, and nurturing kittens. Music is her greatest passion, leading her to become an accomplished pianist. The wealthy neighbor, Mr. Laurence, noticing her talent and kindness, gifts her his deceased granddaughter's piano, forging a close bond between them.

Her compassion extends beyond her family. During the Confederate occupation, Beth and her sisters help hide a runaway slave named John. She also rescues and nurses an abandoned kitten, Milky Ann, who becomes a beloved household member.

Beth contracts scarlet fever while aiding a poor family. Though she survives, the illness leaves her permanently weakened. As the story progresses, her health gradually declines. She continues small kindnesses, like knitting for children, but eventually grows too frail even for these tasks, finding her sewing needle "so heavy." She dies at twenty-three in her mother's arms. Her death profoundly impacts her sisters, especially Jo, who resolves to live more selflessly in her memory.

Throughout her life, Beth remains content with domesticity, expressing no desire for marriage or worldly ambitions. She persists as the family's stabilizing and moral force until her death, leaving a lasting legacy of kindness and self-sacrifice.