The rhodium complex HRhCO(PPh3)(3) encapsulated into the pores of hexagonal mesoporous silica (HMS) by in situ synthesis (Rh-HMS) was found to be an efficient heterogeneous catalyst for the hydroformylation of C-5-C-12 olefins. The (Rh-HMS) catalyst system was thoroughly characterized by P-XRD, (PCP)-P-31-MAS NMR, FT-IR, TGA, SEM and N-2 adsorption/desorption techniques. The P-31 CP-MAS NMR spectrum of Rh-HMS shows that the HRhCO(PPh3)(3) complex encapsulated into the pores of HMS without decomposition, indicating that the pores of the catalyst system act as nanophase reactors. The detail investigations were performed on the effects of temperature, amount of catalyst, partial pressure of CO and H-2 and weight ratio of HRh(CO)(PPh3)(3) to TEOS for the hydroformylation of 1-hexene. At lower temperature the selectivity and n/iso ratio of aldehydes was higher. The selectivity and n/iso ratio of aldehydes was increased on increasing the amount of HRhCO(PPh3)(3) complex into the HMS. The catalyst had shown good thermal stability and recyclability. The catalyst was recycled giving excellent conversion (100%) for the hydroformylation of 1-hexene. (C) 2008 Elsevier B.V. All rights reserved.