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 sub(1) = 1.05(2) M sub(middot in circle), M sub(2) = 0.89(2) M sub(middot in circle), R sub(1) = 1.38(2) R sub(middot in circle), R sub(2) = 1.28(2) R sub(middot in circle), log(L sub(1)/L sub(middot in circle)) = 0.258, and log (L sub(2)/L sub(middot in circle)) = 0.117, and the separation of the components was determined to be a = 3.333(16) R sub(middot in circle). Newly obtained parameters yield the distance of the system as 136(8) pc. Analyses of the mid-eclipse times indicate a period increase of (P/P) = 4 x 10 super(7) yr that can be interpreted in terms of the mass transfer (dM/dt) = 5 x 10 super(-8) M sub(middot in circle) yr super(-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).