Recently, Type IV self-dual codes over rings of order 4 have been introduced as self-dual codes over the rings with the property that all Hamming weights are even. All Type IV self-dual codes over Z 4 of lengths up to 16 are known. In this paper, the classification of such codes of length 20 is given. The highest minimum Hamming, Lee and Euclidean weights of Type IV Z 4 -codes of lengths up to 40 and length 56 are also determined.