Chimney structures are predominantly subjected to wind loads. Hence, it is crucial to design them considering the complex fluid-structure interactions under wind loads. In this paper, we investigate the aeroelastic behaviour of a typical tall RC chimney (referred to as principal chimney) in isolated and interference conditions. Systematic studies have been carried out with varying diameters of the interfering chimney (0.75, 1, 1.25 times the diameter of principal chimney) to understand the change in aeroelastic behaviour. The dimensions of the principal chimney considered are taken from a typical power plant in India, with a uniform diameter of 10.41 m and a height of 124.5 m. To perform the wind tunnel experiments, geometric model scale of 1:250 was adopted. The interfering chimney was placed at angles of 0, 5, 10, 15, 20, and 90° with respect to the incoming wind direction, and experiments were conducted with wind speeds ranging from 8.24 to 32.32 m/s. The along- and across-wind behaviour of the principal chimney in isolated and three interference conditions were discussed. As expected, the mean along-wind bending moments in the interference conditions were found to be less than isolated condition due to the shielding effect. With increase in angle of attack in the interference condition, recovery of the mean bending moments was observed. In the case of across-wind behaviour, the critical velocity was noted to shift with varying diameters of the interfering chimney.