Abstract. We proved in [K. Abe, K. Fukui, On commutators of equivariant diffeomorphisms, Proc. Japan Acad. 54 (1978), [52][53][54] that the identity component Diff r G,c (M )0 of the group of equivariant C r -diffeomorphisms of a principal G bundle M over a manifold B is perfect for a compact connected Lie group G and 1 ≤ r ≤ ∞ (r = dim B + 1). In this paper, we study the uniform perfectness of the group of equivariant C r -diffeomorphisms for a principal G bundle M over a manifold B by relating it to the uniform perfectness of the group of C r -diffeomorphisms of B and show that under a certain condition, Diff r G,c (M )0 is uniformly perfect if B belongs to a certain wide class of manifolds. We characterize the uniform perfectness of the group of equivariant C r -diffeomorphisms for principal G bundles over closed manifolds of dimension less than or equal to 3, and in particular we prove the uniform perfectness of the group for the 3-dimensional case and r = 4.