Two　lignin-containing　cellulose　nanofibril　(LCNF)　samples,　produced　from　two　unbleached　kraft　pulps　with　very　different　lignin　contents,　were　used　to　produce　reinforced　polyvinyl　alcohol　(PVA)　hydrogels.　The　effects　of　LCNF　loading　(0.25-2　wt　%)　and　lignin　content　on　the　rheological　and　mechanical　properties　of　the　reinforced　hydrogels　were　investigated.　The　2　wt　%　LCNF-reinforced　PVA　hydrogels　exhibited　up　to　a　17-fold　increase　in　storage　modulus　and　a　4-fold　increase　in　specific　Young＇s　modulus　over　that　of　pure　PVA　hydrogel.　Both　the　mechanical　and　rheological　properties　of　LCNF-reinforced　PVA　hydrogels　can　be　tuned　by　varying　LCNF　loading　and　LCNF　lignin　content.　During　LCNF　production,　lignin　reduced　cellulose　depolymerization,　resulting　in　LCNF　with　high　aspect　ratios　that　promoted　entanglement　and　physical　bridging　of　the　hydrogel　network.　Free　lignin　particles　generated　during　LCNF　production　acted　as　multifunctional　nanospacers　that　increased　porosity　of　the　hydrogels.　Because　LCNFs　were　produced　from　unbleached　chemical　pulps,　which　have　high　yields　and　do　not　require　bleaching,　this　study　provides　a　more　sustainable　approach　to　utilize　lignocelluloses　to　produce　biomass-based　hydrogels　than　by　methods　using　commercial　bleached　pulps.　©　2018　American　Chemical　Society.