A good amount of work has been done on degree of approximation of functions
belonging to $Lipalpha ,;Lipleft( {alpha ,r} ight),Lipleft({xi left( t ight),r} ight)$ and $ Wleft( {{L_r},xi left( t
ight)} ight)$ classes using Ces$grave{a}$ro, N$ddot{o}$rlund and generalised N$ddot{o}$rlund single summability methods by a
number of researchers (cite{ga}, cite{sg}, cite{qn}, cite{kq1}, cite{kq2}, cite{pc}, cite{hk}, cite{ll}, cite{br}). 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 Lipleft( {alpha ,r} ight)$ class and $ f in ;Wleft( {{L_r},xi left( t ight)} ight)$ class by $(N,p_{n})(C,1)$ product summability means of its Fourier series.

Keywords: Degree of approximation, $ Lipleft( {alpha ,r} ight) $ class,
$ Wleft({{L_r},xi left( t ight)} ight) $ class of functions, $(N,p_{n})$ mean, (C,1) mean, $(N,p_{n})(C,1)$ product means,
Fourier series, Lebesgue integral