Big Bang Nucleosynthesis is a reliable cosmological test
of physics beyond the Standard Model and in particular of possible
non-standard neutrino characteristics. We present a short review of
several modified BBN models including beyond Standard Model neutrino
physics. First we present a short review of cosmological effects of
additional relativistic sterile neutrino $\nu_s$ and constraints on
it following from the standard BBN model and from BBN with
non-equilibrium $\nu_e \leftrightarrow \nu_s$ oscillations. Then we
discuss BBN model with $\nu_e \leftrightarrow \nu_s$ oscillations
and the cosmological constraints on oscillations parameters. Finally
BBN with $\nu_e \leftrightarrow \nu_s$ oscillations and lepton
asymmetry bigger than the baryon one is described. The interplay
between $\nu_e \leftrightarrow \nu_s$ oscillations and lepton
asymmetry in the neutrino sector and its BBN effect are presented.
In particular, we discuss asymmetry generation by non-equilibrium
resonant $\nu_e \leftrightarrow \nu_s$ neutrino oscillation. We
discuss also the capability of relic lepton asymmetry to enhance
neutrino oscillations due to spectrum wave resonance of neutrinos.
Cosmological constraints on active-sterile neutrino oscillations for
different values of the lepton asymmetry and for different initial
population of $\nu_s$ are presented.