The whitening effect, tyrosinase inhibition, and cytotoxicity of neoagarotetraose were measured after its purification from hydrolyzed agar by gel filtration chromatography. In melanoma B16F10 cells, the melanin content of neoagarotetraose-treated cells was the same as that treated by kojic acid or arbutin. In addition, tyrosinase of melanoma cells was strongly inhibited by neoagarotetraose at a concentration of $1{mu}g/ml$ and similarly inhibited at 10 and $100{mu}g/ml$ compared with those by arbutin or kojic acid. The activity of mushroom tyrosinase showed a 38% inhibition by neoagarotetraose at $1{mu}g/ml$, and this inhibitory effect was more efficient than that by kojic acid. Neoagarotetraose revealed a similar $IC_{50}$ (50% inhibition concentration) value for mushroom tyrosinase as that by kojic acid. These data suggest that the neoagarotetraose generated from agar by recombinant $eta$-agarase might be a good candidate as a cosmetic additive for the whitening effect.