1. Introduction. Quasi-quadratic residue codes (QQR codes) are a family of binary linear codes. They were first introduced by Bazzi and Mitter[2] as a quasi-cyclic code. Their work set foundations for the study of QQR codes. They discovered the relation between weights of a QQR code and number of points on hyperelliptic curves. Joyner [8] built upon this relation, and revealed the link between the QQR code and the famous Goppa's Conjecture in coding theory.We are interested in these codes mainly for two reasons: Firstly, they have close relations with hyperelliptic curves and Goppa's Conjecture, and serve as a strong tool in studying those objects. Secondly, they are very good codes. Computational results show they have large minimum distances when p ≡ 3 (mod 8).QQR codes are similar to quadratic residue codes. They are asymptotically rate half codes (exactly rate half when p ≡ 3 (mod 4)). Also, as we will show, P SL 2 (p) acts as automorphisms of the extended QQR codes in a similar way as of the extended quadratic residue codes. Furthermore, when p ≡ 7 (mod 8), we will show that the QQR code is equivalent to the even subcode of the corresponding quadratic residue code direct sum with itself, and therefore their weight enumerators have close relations.We will utilize the result that P SL 2 (p) acts on these codes to prove a new discovery about their weight polynomials, i.e. they are divisible by (x 2 + y 2 ) d−1 , where d is the corresponding minimum distance. The proof uses shadows of codes, a powerful tool to study weight polynomials. We also apply this idea to quadratic residue codes, and prove that their weight polynomials are divisible by (x + y) d , with d being the minimum distance.These results impose strong conditions on the weight polynomials of quadratic residue codes and QQR codes. Combining the divisibility result and Gleason's Theorem, we can derive an efficient algorithm to compute the weight polynomials of QQR codes. We also use these results to correct the existing computational