A single-phase transesterification of linseed oil has been investigated in the presence of heterogeneous base catalyst (CaO) with different co-solvents and hydrogel as a water absorber. Di-ethyl ether, tetrahydrofuran, biodiesel, n-hexane were depleted as co-solvents to improve the mutual solubility of the oil and methanol. The molar ratio of methanol to oil, the molar ratio of co-solvent to methanol, and catalyst concentration are among the integral parameters that influence the FAME yield. The results of transesterification processes with co-solvent and without co-solvent were compared with each other, thus, T-test and F-test depicted striking level of modification. Response surface methodology was carried out to optimize the main process parameters. The maximum FAME yield of 98.77% was reached under the following optimum conditions: molar ratio of methanol to oil 9.41:1, molar ratio of DEE to methanol of 1.11:1, catalyst concentration of 0.98 wt%, temperature of 30 degrees C, agitation rate of 650 rpm, and reaction time of 60 min. (C) 2019 Elsevier Ltd. All rights reserved.