The ultrafast excited state relaxation dynamics of all-trans-Astaxanthin (AXT) in Dimethyl Sulfoxide (DMSO) was investigated using femtosecond time-resolved transient absorption and multiplex transient grating spectroscopies. The results reveal that the S0→S2 absorption transition directly occurs in the AXT/DMSO system, which corresponds to the ground state bleach in the 420~550 nm spectral region. Internal conversion that is ascribed to S2→S1 transition takes place on the time constant of 120~160 fs. The excited state absorption of the S1 state corresponds to the region of the 550~740 nm. The recovery progress of the ground state bleach corresponds to the internal conversion progress, which is attributed to the S1→S0 transition and occurs on the time scale of 4.50~5.50 ps.