We study the number of limit cycles of the polynomial differential systems of the forṁ x = y − f 1 (x)y,ẏ = −x − g 2 (x) − f 2 (x)y, where f 1 (x) = εf 11 (x) + ε 2 f 12 (x) + ε 3 f 13 (x), g 2 (x) = εg 21 (x) + ε 2 g 22 (x) + ε 3 g 23 (x) and f 2 (x) = εf 21 (x)+ε 2 f 22 (x)+ε 3 f 23 (x) where f 1i , f 2i and g 2i have degree l, n and m respectively for each i = 1, 2, 3, and ε is a small parameter. Note that when f 1 (x) = 0 we obtain the generalized polynomial Liénard differential systems. We provide an accurate upper bound of the maximum number of limit cycles that this differential system can have bifurcating from the periodic orbits of the linear centerẋ = y,ẏ = −x using the averaging theory of third order.