Anaerobic digestion of the organic fraction of municipal solid wastes is a well-established process for biogas production and various forms of pre-treating the biomass have been evaluated to increase the methane yield. The present study evaluated the pre-treatment of 14 fruits and vegetables wastes (FVW) samples from a central food distribution market, using sodium hydroxide (NaOH), varying the concentration (3 and 6%) and exposure time (24 and 48 h) to the alkali reagent. The biochemical methane potential (BMP) assays of the pretreated and untreated wastes were carried out under mesophilic conditions (37 ºC). Biogas generation by the residues treated with 3% NaOH generated an average of 65% more methane (≈127 NmLCH4.gVS−1) as compared to the untreated waste (77 NmLCH4.gVS−1) and 25% more than that treated with 6% NaOH (102 NmLCH4.gVS−1). Thus, we observed that doubling the pretreatment time and concentration of the chemical reagent did not result in greater methane production. This behavior could have been associated with the presence of some compounds (sodium, pesticides, etc.) that have an inhibitory effect in the aqueous solution. Finally, this study confirmed that the optimal conditions for the pretreatment and biodigestion phases must be reevaluated according to the nature of the substrate evaluated.Graphical abstract