Suppose \(n<5p\) when \(p \in (1, 2)\) and \(n<p+\frac{4p}{p-1}\) when \(p \ge 2\) . We establish an a priori Hölder estimate for regular stable solutions to nonlinear equations involving p-Laplacian \(-\Delta _p u = f(u)\) , where \(f \in C^1(\mathbb {R})\) satisfies \(f(t)\ge -A|t|^{\gamma }-K\) for all \(t\in \mathbb {R}\) with some nonnegative constants A, K and \(\gamma \) . Furthermore, when \(p=2\) we obtain the local Hölder regularity for stable energy solutions. Notice that the dimension range \(n<p+\frac{4p}{p-1}\) is optimal when \(p \ge 2\) .