Medford-based Century Bancorp Inc. said second-quarter net income rose 13.7 percent to $4.78 million, compared with of $4.2 million in the same period a year ago.

Net income for the first six months of the year rose to $8.58 million, up 8.3 percent from $7.9 million in the same period last year.

Total assets increased 9.4 percent from $2.7 billion at Dec. 31, 2011 to $3 billion at June 30.

Century Bancorp is the parent of Century Bank and Trust Co., which has 24 full-service branches in Greater Boston.

Century Bancorp’s provision for loan losses decreased by $400,000 from $2.4 million for the six months ended June 30 to $2 million, mainly as a result of changes in the composition of the loan portfolio.

The company realized net gains on sales of investments of $590,000 in the first six months of this year, compared with $362,000 for the same period in 2011.

Its allowance for loan losses was $18 million, or 1.75 percent of loans outstanding at June 30, compared with $16.6 million or 1.68 percent of loans outstanding at Dec. 31, 2011, and $15.9 million, or 1.65 percent of loans outstanding at June 30, 2011. Non-performing assets totaled $5.3 million at June 30, compared with $7 million at Dec. 31, 2011 and $12.3 million at June 30, 2011.

The company’s board of directors voted to pay a regular quarterly dividend of 12 cents a share on the company’s Class A common stock, and 6 cents a share on the company’s Class B common stock. The dividends were declared payable Aug. 15 to stockholders of record on Aug. 1.