Effects of surfactant on the lateral motion of bubbles in linear shear flows are numerically investigated by using an interface tracking method. Ranges of the bubble Reynolds number Re, Eotvos number Eo, Morton number M and dimensionless shear rate Sr are 2 < Re < 70, 0.6 < Eo < 5, 10(-6) < M < 10(-4) and 0 <= Sr < 1, respectively. The main conclusions obtained are as follows: (1) the lift coefficient, C-L, of a bubble decreases as the Langmuir number increases, (2) the surfactant decreases the critical values of Eo and Re, at which C-L changes its sign. (3) the reduction in C-L of bubbles of large Hatta numbers due to the presence of surfactant can be understood from the surface tension reduction, and (4) the Marangoni force affects C-L of small Hatta number bubbles, and therefore, the surface immobilization effect of the Marangoni force should be taken into account to model C-L of contaminated bubbles. (C) 2017 Elsevier Ltd. All rights reserved.