Purpose: Aerial spraying with an agricultural unmanned helicopter became a new paradigm in the agricultural practice. Laterally tilting behavior of a conventional agricultural helicopter, resulting in the biased down-wash and uneven spray deposit is a physically intrinsic phenomenon while hovering and cruise flights. Authors studied and developed a roll-balanced agricultural helicopter with a raised pylon tail rotor system. In this study, the attitude of the roll-balanced helicopter was determined using the Kalman filter algorithm, and the quality of roll balancing of a bare-airframe helicopter was evaluated. Methods: Instantaneous attitudes were estimated using the advantage of gyroscope, followed by the long term correction and prediction using accelerometer data for the advantage of convergence. The attitudes of the fuselage were calculated by applying the Kalman filter algorithm. The spraying maneuver of the helicopter was performed at a field of 50 m long, and the attitude data were acquired and evaluated. Results: The determination of attitude using the inertial measurement unit(IMU) and Kalman filter was reliable and practical. The intrinsic attitude of the developed helicopter was stable and roll-balanced. The deviation of roll angle was ${pm}6.3^{circ}$ with an average of $0^{circ}$, referring to roll-balanced. Conclusions: Handling quality of the roll attitude determined to be steadily balanced. The balancing behavior of the developed helicopter would result in an even spray pattern during aerial application.