Aggregation of single-walled carbon nanotubes (SWCNTs) is one of the major obstacles for many nanotube fundamental studies and practical applications, such as nanocomposites, electronic devices, bioimaging, biosensors, and drug-delivery. In this study, two types of SWCNT samples, enriched with (6,5) and (7,5) chiral structures, respectively, were investigated. SWCNT suspensions containing various fractions of bundles were obtained by ultracentrifugation. Dialysis was used to achieve the controlled nanotube rebundling. Results showed that SWCNT photoluminescence (PL) sidebands (the transverse sideband E12,21, the phonon coupled sidebands E22 + G,G′, and the E33 → E11 emission band) are dependent on the nanotube aggregation. We proposed that SWCNT exciton relaxation routes increase upon nanotube aggregation, resulting in the suppression of primary PL peaks and the enhancement of PL sidebands. Furthermore, the correlation between PL sidebands and nanotube aggregation was also demonstrated in diverse dispersion conditions involving different surfactants and solvents. These results highlight the potential of employing PL sidebands as a sensitive characterizing tool to monitor the nanotube aggregation under different circumstances.