We have systematically studied the pressure ( P) effects on the normal state resistivity and on the superconducting transition temperature T c for the series of (Nd 1− x Pr x )Ba 2Cu 3O 7. Our results show that the functions T c( x) and d T c/d P( x) are not directly related to each other, suggesting that the factor controlling the x-dependent T c in (Nd 1− x Pr x )Ba 2Cu 3O 7 is not sensitive to pressure. However, we have found that the x dependency of d T c/d P is strongly correlated to the x dependency of the pressure effect on carrier concentration. We therefore attribute the origin of pressure-induced T c variation in (Nd 1− x Pr x )Ba 2Cu 3O 7 to a combined effect of pressure-induced charge transfer and pressure-induced hole depletion.