In this paper, I have discussed the description of nature which controls both courtly elements and human beings in Chaucer's Troilus and Criseyde. First, as for the description of natural objects, the relationship between the cloud and the star reflects Criseyde's black dress and her bright figure. Furthermore, the description of natural objects shows the delicate feelings of the characters; in particular, "the sonne bright" represents a joyous state of mind. The fatal 'reyn' heightens the drama as the story develops. The rain, governing the human beings and the palace, facilitates the love affair between Troilus and Criseyde. However, when Troilus and Criseyde go against nature, she does not support them, as is shown in the fact that they complain of the day and night at the end of Books III and IV. Second, the plants also reflect the delicate emotions of the characters. The descriptions of plants suggest the harmonious development of the love affair in Books I, II, and III, as the adjectives "newe grene," "fresshe", "blew and white and rede," and "lusty" show, while they may show that in Book IV the natural order is about to break down, as in the expressions: "til the tree be bare" and "the blak bark of care," the adjectives reminding us of the severe winter and the coldness of the human beings. However, the description of Phebus as "gold-tressed" signals a return to the harmony of nature in Book V. In spite of the characters' tragic end, nature remains undisturbed. Finally, the animals are also deeply connected with the characters in this work: "the newe abaysed nyghtyngale" is compared to Criseyde, "an egle, fethered whit as bon" in Criseyde's dream suggests the manly figure of Troilus, and the "bor" in Troilus's dream is associated with Diomede. In this way, the descriptions of nature in Troilus and Criseyde mirror faithfully the actions and states of minds of the characters.