Frei was successful as a ski racer in the late 1960s and early 1970s, particularly in the slalom competitions. At the 1968 Winter Olympics of Grenoble he participated in the slalom competition and was at the competitions in Chamrousse tenth. In the World Cup he was able to place in the points between January 1968 and February 1971. The Swiss achieved his best result in the World Cup by finishing third in the Wengen slalom in the 1968/69 season . In the same season Frei achieved his best results in these ratings with 23rd place in the overall World Cup and 12th place in the Slalom World Cup. Frei also competed in the slalom at the Alpine World Ski Championships in 1970 in Val Gardena and came in seventh. In 1971 he won the title of Swiss slalom champion .