This paper concentrates on
scriptH∞$$ {\mathcal{H}}_{\infty } $$ state‐feedback control problem for a kind of Markov jump nonlinear systems with generally uncertain transition rates. The nonlinearity satisfies the sector condition, which is more generic than the ordinary Lipschitz nonlinearity. First, a
scriptH∞$$ {\mathcal{H}}_{\infty } $$ performance criterion is derived for the closed‐loop systems. Next, based on the proposed performance criterion and a judicious method of using inequalities, a novel controller synthesis method is developed in terms of linear matrix inequalities. Compared with the existing result, the proposed method significantly reduces the conservativeness of the controller synthesis. Finally, a numerical example is provided to show the validity and merit of the developed result.