Isotope shifts Δσ^148,154 in 200 spectral lines of neutral samarium atom (Sm I) in the region of 355−455 nm (28160−21970 cm^-1) have been measured using a Fourier Transform Spectrometer. Isotope shift data in 187 spectral lines of Sm I are being reported for the first time. Level isotope shifts, ΔT^148,154 of 119 high odd- and 7 low even-parity energy levels have been evaluated using present isotope shift data combined with the earlier available data. These ΔT^148,154 values have enabled us to check the assignments to 4f⁶6s6p and 4f⁵5d6s² configurations of the odd-parity levels made earlier on the basis of parametric calculations. For several levels, the reported compositions of the mixed configuration of type [4f⁵(⁶H⁰, ⁶F⁰) 5d6s² + 4f⁶(⁷F) 6s6p(³P⁰)] have been interpreted with the help of our ΔT^148,154 values. 20 unassigned energy levels have been uniquely assigned to 4f⁵5d6s² configuration. The present study provides ΔT^148,154 values of the levels, which were tentatively assigned to 4f⁵5d²6s and 4f⁶5d6p configurations. We could also identify 4f⁶5d6p configuration for 12 unassigned levels.