There are many changes for protein molecules in conformations in the process of folding．The mean-square radius of gyration and its distribution function P(S) were calculated by using the exact enumeration calculation method．It was found that the dimension was large at the beginning of folding

and the range of its distribution was also wide．However

the dimension became small and compact at the end of folding

and the range of its distribution also became small．The mean-square radius of gyration 〈S2〉t with the number of contacts t is shown as〈S2〉t／Nl2=a+bN where a depends on the number of contacts (t) and b is independent of the number of contacts (t)

and N is the chain length of two-dimensional protein molecules．There are different distributions for various residue sequences. The value of P(S) nearby the mean-square radius of gyration is more large for the folding sequence．A ratio of SN／DN was also calculated．SN is the number of designing sequences

and DN is the number of designable conformations．It was found that the ratio may be expressed as -1.684+0.3255N ≤ SN／DN ≤ -0.8664+0.3125 N (N ≥ 13) These results may provide some insights into the folding of proteins molecules．