  The observational and theoretical status of neutrino oscillations in
connection with solar and atmospheric neutrino anomalies is presented in brief.
The effect of neutrino oscillations on the early Universe evolution is
discussed in detail. A short review is given of the standard Big Bang
Nucleosynthesis and the influence of resonant and nonresonant neutrino
oscillations on active neutrinos and on primordial nucleosynthesis of He-4. BBN
cosmological constraints on neutrino oscillation parameters are discussed.
