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We present the results of observations of the very low surface brightness (VLSB) dwarf galaxy SDSS J092609.45+334304.1 with extreme parameters which indicate its unevolved status. Namely, its value of O/H, derived as an average of that in two adjacent H  ii  regions at the NE edge of the disc, corresponds to the parameter  12 + log(O/H) = 7.12 ± 0.02 , which is amongst the two lowest known. The total H  i  flux measurement obtained with the Nançay Radio Telescope and the photometric results implies that the galaxy ratio M(H  i )/  L  B ∼ 3.0  is among the top known in the Local Volume. The galaxy is situated in the region of a nearby underdense region known as the Lynx–Cancer void, where other unevolved galaxies, including DDO 68, HS 0832+3542 and SAO 0822+3545, are known to be present. The total mass of this almost edge‐on VLSB galaxy is ∼8.3 times larger than its baryonic mass, implying the dynamical dominance of dark matter (DM) halo. The  ( u − g ), ( g − r )  colours of the outer parts of this galaxy are consistent with the ages of its main stellar population of 1–3 Gyr. Thanks to the galaxy isolation, the small effect of current or recent star formation, its proximity and rather large H  i  flux (∼2.5 Jy km s −1 ), this VLSB dwarf is a good laboratory for the detailed study of DM halo properties through H  i  kinematics and the star formation processes in very metal‐poor low surface density environment. This finding, along with the discovery of other unusual dwarf galaxies in this void, provides evidence of the relation between galaxy evolution and its very low‐density environment for the baryonic mass range of 10 8  to  10 9  M ⊙  . This relation seems to be consistent with that expected in the Λ cold dark matter models of galaxy and structure formation.

SDSS J092609.45+334304.1: a nearby unevolved galaxy