12. Divisible by 3, and the digits of each number are limited to $1, 2, 3$ (1, 2, 3 do not have to be all used) all natural numbers less than 200000 are $\qquad$
$\qquad$
12. The only one-digit number that can be divided by 3 and is composed of only the digits 1, 2, 3 is 3.

The two-digit numbers that can be divided by 3 and are composed of only the digits $1, 2, 3$ can be obtained as follows: arbitrarily write one of $1, 2, 3$ in the tens place, then configure the units digit based on the remainder of the tens digit divided by 3. If the remainder is 0, write 3 in the units place; if the remainder is 1, write 2; if the remainder is 2, write $1. \therefore$ There are 3 such two-digit numbers.

Similarly, the number of three-digit, four-digit, and five-digit numbers that meet the conditions are $3^{2}, 3^{3}, 3^{4}$ respectively. For six-digit numbers that meet the conditions, the first digit must be 1, thus there are $4^{4}$ such numbers.

Therefore, the total number of natural numbers that meet the conditions is $1+3+3^{2}+3^{3}+2 \times 3^{4}=202$.