This paper reports the hydroformylation of 1-butene catalyzed by RhCI(CO)(TPPTS)(2) (TPPTS: P(m-C6H4SO3Na)(3)) and BISBIS (sodium salt of sulfonated 2,2'-bis(diphenylphosphinomethyl)-1,1'-biphenyl) in aqueous/organic two-phase catalytic system. The effects of reaction parameters on the catalytic activity and regioselectivity were investigated under the optimum reaction conditions: 130 degreesC, 2.5 MPa (syngas pressure), [BISBIS]/[Rh] = 5, [1-butene]/[H-2]/[CO] = 1:1:1, [1-butene]/[Rh] = 10 400, TOF and the regioselectivity for n-valeraldehyde were 2987 h(-1) and 98%, respectively. (C) 2003 Elsevier B.V. All rights reserved.