The thermal conductivity λ and the specific heat cp of Ba2YCu3O7-x and La2CuO4 have been measured in the temperature range 0.03 < T < 30 K. The thermal conductivity of sintered Ba2YCu3O7-x samples varies as T2 between 0.7 and 8 K, While below 0.3 K λ (T) is described as a sum of two terms Where one is proportional to T and the other varies like T3. For sintered La2CuO4, λ (T) is distinctly smaller than in sintered Ba2YCu3O7-x in the Whole temperature range. The specific heat of both compounds shows a non-vanishing linear term γ T between 1.4 K and 15 K, Where γ in sintered Ba2YCu3O7-x is nearly an order of magnitude larger than in crystalline La2CuO4. © 1988 Elsevier Science Publishers B.V.