A one-factor field experiment established by means of random block sampling (four series have been applied) was conducted at the Mountain Experimental Station in Czyrna, near Krynica. Naked and covered oat of Dukat and Akt varieties were sown on 20 m2 plots in the amount of 650 seeds of full germination capabilities per 1 m2. To evaluate oat reaction to thermal and rainfall conditions a method which implied dividing oat cultivation and vegetation time into 5 agrophenological periods was applied. The successive periods were: 1) before sowing, 2) from sowing to emergence 3) from emergence to propagation, 4) from propagation to heading, and finally 5) from heading to wax maturity. The research has been aimed at determining thermal and rainfall conditions influence upon the yielding capacity of naked and covered oat cultivated in the mountainous conditions of Low Beskid. Vegetation seasons with regards to recorded rainfall in the years of research were found to be average in years 2000 and 2002, and very wet in 1999 and 2001; the total rainfall reached in the respective years the following values: 453.4 mm, 424.5 mm, 587.1 mm, and 678.2 mm. The research revealed that both naked and covered oat gave the highest yield in the years in which the total rainfall summarised over the respective phenophases was very close to the optimal one declared for not-mountainous areas. Naked oat, in comparison to covered oat, did not react by worse emergence to a smaller rainfall in a pre-sowing period. For naked oat grain shattering induced by rainfall in the full maturity phase was nearly 3 times higher than for covered oat. A delay in the sowing date resulted in a lower amount of grain in a panicle.