A good amount of work has been done on degree of approximation of functions belonging to Lip${alpha}$, Lip($xi$(t),r) and W($L_r,xi(t)$) and classes using Ces$`{a}$ro, N$"{o}$rlund and generalised N$"{o}$rlund single summability methods by a number of researchers ([1], [10], [8], [6], [7], [2], [3], [4], [9]). But till now, nothing seems to have been done so far to obtain the degree of approximation of functions using (N,$p_n$)(C, 1) product summability method. Therefore the purpose of present paper is to establish two quite new theorems on degree of approximation of function $f;in;Lip({alpha},r)$ class and $f;in;W(L_r,;xi(t))$ class by (N, $p_n$)(C, 1) product summability means of its Fourier series.