The landmark strike at the Millennium Stadium puts Williams ahead of All Blacks great Doug Howlett and into joint-third place alongside former England flying wing Rory Underwood on the all-time try-scoring list.
But Williams, who has struck 48 times for Wales and twice for the Lions, insists there is plenty more to come.
"It's a great honour and I'm really pleased to score 50 tries," said Williams, who scored twice for Ian McGeechan's 2009 Lions in the historic third-Test win over South Africa.
"It will be great to tell the children and grandchildren when I hang the boots up but I am just as happy when I scored my first try for Wales.
"The accolade of scoring the number of tries is just a bonus to me and I won't let the feat affect me. I never expected it would happen and it still feels mad. I don't want to get carried away because I feel there is more tries in me.
"Hopefully I get picked to face Australia next weekend and if I score to become the greatest in the northern hemisphere, then I'll be a happy man."
Only Japan's Daisuke Ohata with 69 tries and Australian legend David Campese stand in the way of Williams becoming the greatest finisher of all-time.
And the 32-year-old current IRB World Player of the Year admits he has Campese, on 64 touchdowns, in his sights ahead of the mouth-watering clash with the Wallabies next Saturday.
"When you look back in history to the likes of Campese, it's a massive honour for me to be mentioned alongside quality players like him," added Williams, whose first Lions tour was in 2005.
"I'm still enjoying my rugby and believe I'm capable of scoring even more - it's my job.
"I want to get up to David Campese one day and I hope number 50 wasn't the last of my tries. I want people to be talking about my 51st and 52nd tries and so on."
World's top ten try-scorers
1. Daisuke Ohata (Japan); Caps - 58; Tries - 69
2. David Campese (Australia); 101; 64
3. Rory Underwood (England and British & Irish Lions); 91; 50
Shane Williams (Wales and British & Irish Lions); 71; 50
5. Doug Howlett (New Zealand); 62; 49
6. Christian Cullen (New Zealand) 58; 46
7. Joe Rokocoko (New Zealand); 60; 45
8. Jeff Wilson (New Zealand) 60; 44
9. Gareth Thomas (Wales and British & Irish Lions); 103; 41
10. Chris Latham (Australia); 77; 40