A new catalyst system is described for producing normal aldekydes predominantly from α-olefins. The catalyst consists of a rhodium compound, triphenyl phosphite and sodium acetate. Effects of various reaction parameters on the ratio of n- to iso-aldehyde are reported. Sodium acetate has been found to be highly selective production of normal isomer and for maintaining the activity of the catalyst for a long period of time. The rate of aldehyde formation depends on the concentration of rhodium as follows: d[aldehyde]/dt∝[Rh]1.0 (at initial state) d[aldehyde]/dt∝[Rh]0.7 (at stationary state) However, the concentration of rhodium has little effect on the n/i ratio.