Internet audience measurement firm comScore Media Metrix said Tuesday that online video-sharing site YouTube broke into comScore’s top 50 ranking of Web sites for the first time in July.

ComScore said YouTube counted 16 million visitors in July, up 20 percent from June. That placed YouTube at No. 40 on ComScore’s top 50 online properties. ComScore also said MySpace Videos saw its traffic double in one month to 20 million unique visitors.

According to Nielsen//NetRatings, YouTube finished July with 30.5 million unique visitors, up from 19.6 million in June. Meanwhile, MySpace clocked in at 18.1 million uniques, an increase from 11.1 million in June, Nielsen said.