In this study we present photometric and spectroscopic variation analysis and an orbital period study of a low-mass interacting system OO Aql. Simultaneous solution of the light and radial velocity curves provides us with the determination of a new set of stellar physical parameters for the primary and the secondary companion, M-1 = 1.05(2) M-circle dot, M-2 = 0.89(2) M-circle dot, R-1 = 1.38(2) R-circle dot, R-2 = 1.28(2) R-circle dot, log(L-1/L-circle dot) = 0.258, and log (L-2/L-circle dot) = 0.117, and the separation of the components was determined to be a = 3.333(16) R-circle dot. Newly obtained parameters yield the distance of the system as 136(8) pc. Analyses of themid-eclipse times indicate a period increase of (P/(P) over dot) = 4x10(7) yr that can be interpreted in terms of the mass transfer (dM/dt) = 5 x 10(-8) M-circle dot yr(-1) from the less massive component to the more massive component. Our new solution confirmed that OO Aql is a multiple system in the form of AB + C + D. We found initial astrophysical parameters for the component of the system and its current age to be 8.6 Gyr using a non-conservative stellar evolution model (EV-TWIN code).