In this paper, we introduce several numerical radius inequalities involving off-diagonal part of 2 × 2 positive semidefinite block matrices and their diagonal blocks. It is shown that if A, B, C ∈ M n (C) are such that A B * B C ≥ 0, then w 2r (B) ≤ 1 2 4rα + A 4r(1−α) 4rα + C 4r(1−α) and w 2r (B) ≤ r α + (1 − α)C r 1−α , for 0 < α < 1, r ≥ 1. Moreover, we establish some numerical radius inequalities for products and sums of matrices.