Arrietty is a 13-year-old Borrower who resides in a hidden home beneath the kitchen floor of an old English country mansion. Unlike many of her tiny peers, she knows how to read and keeps a diary, giving her a highly curious and restless nature. She resents her parents' strict rules about staying hidden and longs for freedom and interaction beyond her cramped, dimly lit world.

Pod is the patriarch of the Clock family and a highly skilled Borrower who quietly provides for his wife and daughter. He scales giant curtains and furniture to retrieve household necessities, using tools like hatpins to maneuver through the sheer drops of the human world. Though naturally cautious and deeply aware of the dangers posed by humans and cats, he proves remarkably adaptable when faced with the challenge of teaching his daughter how to survive.

Homily is Arrietty's mother and a dedicated homemaker who takes immense pride in her floorboard residence. She decorates her tiny home with repurposed human artifacts, using blotter paper for carpets and coins for plates. Her love for domestic comfort makes her terrified of emigration, and she constantly worries about the physical safety of her husband and the rebellious spirit of her daughter.

The boy is a sickly but highly observant child staying at his great-aunt's rambling English manor. Feeling isolated and angry at his strict treatment by the household staff, he spends much of his time alone in the house and gardens. His discovery of the tiny people living in the house gives him a secret focus and challenges his understanding of the natural order.

Mrs. Driver is the grumpy and suspicious cook and housekeeper of the country mansion. She dislikes having a young boy in her orderly domain and constantly suspects him of mischief or theft. She prefers spending her time drinking madeira wine with the gardener while keeping a sharp, cynical eye out for anything amiss in the household.

Mrs. May is a practical, older woman who rents a room in Kate's family home. Despite her no-nonsense demeanor and focus on traditional homemaking tasks, she harbors a deep appreciation for the fantastic. She uses her memories of her brother's childhood in the countryside to pass down an engaging legend about tiny people living under the floorboards.

Kate is a wild and willful human girl living in a modern London home. She acts as the eager audience for Mrs. May's tale, representing the reader's own curiosity. Her tendency to lose small items like safety pins and crochet hooks prompts the entire story of the tiny floorboard dwellers.

Great Aunt Sophy is the elderly, bedridden owner of the sprawling country estate. She spends most of her days isolated in her room, frequently indulging in Fine Old Pale Madeira. Because of her drinking, she naturally assumes any unusual sights, including tiny men scaling her furniture, are merely alcohol-induced hallucinations.

Crampfurl is the gardener at the country estate. He spends much of his free time indoors, sharing wine and gossip with Mrs. Driver in the kitchen. He generally follows her lead in suspecting the boy of causing trouble around the vast property.

Uncle Hendreary is Pod's brother and a legendary figure within the Clock family. Forty-five years ago, his decision to walk across a highly visible drawing-room mantelpiece led to him being seen by a human. The resulting panic caused his family to flee the comfortable house to live outdoors in a badger den, serving as a constant reminder of the perils of discovery.

Aunt Lupy is Hendreary's wife and Homily's sister-in-law. She is currently living a rough, outdoor lifestyle in a badger den with her husband and sons. Homily views her as somewhat wild and cannot fathom the idea of sharing a kitchen with her in the wild.

Eggletina is Hendreary and Lupy's daughter. Because her parents tried to completely shield her from the truth about the dangers of the human world, she grew deeply curious. One day, she slipped out of an unlatched gate to explore and never returned, leaving her family to presume she was eaten by the household cat.