Beatrice looked a picture of modern elegance in a floral dress by cool girl designer The Vampire's Wife, while Eugenie wore a modest nude Sandro dress with a pleated skit.
The daughters of the Duke and Duchess of York opted for headwear by Alice bands.
Princess Eugenie took to Instagram this morning to share her own special snapshots of the day, writing: "This afternoon, my sister and I attended a Garden Party at Buckingham Palace in support of Her Majesty.
"I really enjoyed meeting such a diverse group of people who were all invited in recognition of their work in their respective communities."