Nick Bailey gave the Addicks an early lead, but two second-half goals from Shane Long, the first from a penalty, then put the Royals in front.
Five minutes from time Charlton skipper Mark Hudson headed the equaliser from a Nick Bailey free-kick.
At kick-off Reading fans had welcomed back two of their former favourites. Winger Glen Little came straight into the team at the start of his loan spell from Portsmouth and there was also home support for Charlton boss Phil Parkinson, one of the most popular players to have worn the Reading shirt.
Dave Kitson, returning from Stoke on loan until the end of the season, has not completed the signing formalities and will not be available for Reading until Saturday.
Charlton's Chinese international Zheng Zhi made only his second start of the season after recovering from a foot injury sustained back in October.
It was the visitors who took a shock lead when leading scorer Bailey turned in a low right-wing cross from Tresor Kandol for his tenth goal of the season.
The home side tried to respond immediately, but Stephen Hunt's shot struck a post and then Kevin Doyle just failed to convert Liam Rosenior's cross.
Reading continued to press forward in search of an equaliser, but again the woodwork came to Charlton's rescue when Kevin Doyle sent a free-kick against the crossbar.
Charlton skipper Hudson literally felt the full force of Reading's attacking effort when he was felled by a ferocious shot from Chris Armstrong, but was able to continue after taking a moment to recover.
Reading defender Alex Pearce was also in trouble from a head wound. He had six stitches inserted during Reading's 2-2 draw at Plymouth on Saturday and the wound re-opened and started seeping blood. Pearce twice had to leave the field in the first half to get treatment.
Fifteen seconds into the second half Reading were back on level terms. Striker Long collected a pass from Doyle and raced towards goal before being brought down by Darren Ward. Long took the penalty himself and gave Charlton keeper Rob Elliot no chance.
Midway through the second half Reading took the lead. Jay Tabb, who had come on as a substitute for Stephen Hunt, sent a right-wing corner into the box where Long thundered a header into the net.
That looked enough to win the game until skipper Hudson's close-range header brought the Charlton equaliser.