A search is performed for a light Higgs boson produced in e+e- collisions at 91 GeV via the Yukawa process e+e- -> b-bbar -> b-bbar A0/ho -> b-bbar tau+tau- which is predicted by CP-conserving two-Higgs-doublet models. Higgs boson masses between 4 to 10 GeV are considered. No evidence is seen for a signal, and upper limits are placed on the parameters xi(A)=tan(beta) and xi(h)=cos(alpha)/sin(beta) which determine the cross sections for the processes involving A0 and ho bosons respectively, in type II two-Higgs-doublet models. The upper limits on xi(A) are in the range 9.3 to 15.6, and the upper limits on xi(h) are in the range 10.6 to 14.1; the precise upper limits depend on the mass of the Higgs boson.